Driven by indefinable uneasiness, Margaret backed her car from the garage, drove southeast out Leghorn Road until a quarter-mile ahead she saw the gray blocks of Electrodyne Engineering.

Beset by an unreasoning alarm she veered down a side road, accelerated and drove wildly for several miles. Then she pulled to the side of the road, and collected her wits. She was behaving erratically, irrationally. Why on earth all these crazy impulses? And these odd sounds in her head, and the peculiar hallucinations?

She made a U-turn and drove back to Leghorn Road. At the intersection she hesitated, then gritting her teeth, turn-ed right toward Electrodyne Engineering.

In the parking lot were Burke's old black Plymouth con-vertible and Dr. Tarbert's Ferrari.

Margaret parked, sat a moment or two in the car. There was no sound to be heard, no voices.

She gingerly alighted, and now ensued another struggle within herself. Should she make use of the main entrance, walk boldly into the general office? Or should she go around to the back and enter through the warehouse?

She chose the warehouse, and circled the building.

The door was as she had left it; she opened it, stepped into the dim interior.

She crossed the concrete floor, her footsteps seeming to echo in spite of her stealth.

Halfway to the workshop she paused weakly, like a swim-mer in the middle of a lake who is uncertain of making the shore.

From the workshop came the murmur of voices, then a hoarse cry of anger—Tarbert's voice.

She ran to the door, looked through.

She was right. Burke was stark staring mad. He had strapped Dr. Tarbert to the bars of his devilish machine; he had fixed heavy contacts to Tarbert's head. Now he was talking, a smile of devilish cruelty on his face. Margaret could catch only a few of his words over the pounding of the blood in her brain, "—rather less pleasant surroundings, on a planet called Ixax—" "—the nopal, as you'll see—" "—relax, now, you'll wake up tauptu—"

"Let me up from here," bellowed Tarbert. "Whatever it is, I don't want it!"

Burke, white-faced and haggard, gave him no more at-tention. He twisted a switch. A wavering bluish-violet glare cast flickering lights and shadows around the room. From Tarbert came an unearthly squeal of pain; he stiffened and strained at the straps.

Margaret watched in horrified fascination. Burke took up a swath of what seemed to be transparent plastic; he threw it over Tarbert's head and shoulders. An apparent rigidity in its folds distended it, held it up from the tubing behind Tarbert's head. To the intermittent flash of the crack-ling light and Tarbert's awful cries, Burke began working and kneading at the transparent film.

Margaret recovered her senses. Gher, gher, gher! She looked about for a weapon, a bar of iron, a wrench, any-thing. . . . There was nothing in sight. She half-started forth to attack him with her bare hands, thought better of it, and instead darted behind Burke into the office, where there was a telephone. Mercifully it was connected. The tone came instantly. She dialed for the operator. "Police, po-lice," she croaked. "Get me the police!"

A gruff masculine voice spoke; Margaret stammered out the address. "There's a madman here; he's killing Dr. Tar-bert, torturing him!"

"We'll send a cruiser over, miss. Electrodyne Engineer-ing, Leghorn Road, right?"

"Yes. Hurry, hurry. . . ." Her voice choked in her throat. She felt a presence behind her; she knew a freezing fear. Slowly, her neck stiff, the vertebrae seeming to grate on each other, she turned her head.

Burke stood in the doorway. He shook his head sorrow-fully, then turned, walked slowly back to where the body of Tarbert lay convulsing, pumping up and down to the flash of the weird lights. He picked up the transparent film, resumed his work—kneading, tugging around Tar-bert's head.

Margaret's legs gave way; she staggered against the jamb of the door. Numbly she wondered why Burke had not injured her. He was a maniac; he must have heard her calling for the police. . .

. Far away she heard the wail of a siren, swelling and singing, louder and louder.

Burke stood up. He was panting; his face was drawn and skull-like. Never had Margaret seen so evil a sight. If she had possessed a gun, she would have shot; if her knees had held her, she would have attacked with her hands. . . . Burke was holding the film bagged around something.

Margaret could see nothing within; nevertheless the sack seemed to move and tremble. Her brain gave a lurch; a black blur covered the bag. . . . She was con-scious of Burke stamping upon the bag—a desecration, she realized; the most hideous act of all.

The police entered; Burke threw a switch on his ma-chine. As Margaret watched numbly the police advanced cautiously upon Burke, who stood waiting, tired and de-feated.

They saw Margaret. "You all right, lady?"

She nodded, but could not speak. She sank down upon the floor and burst into wild tears. Two policemen carried her to a chair and tried to soothe her. Presently an ambulance arrived.

Orderlies carried out the unconscious form of Dr. Tarbert; Burke was taken away in the police cruiser; Mar-garet rode in another, with a trooper driving behind in Mar-garet's own car.

IX

burke was ordered to the State Asylum for the Criminally Insane for observation, and there confined in a small white room with a pale blue ceiling. There was tempered glass in the windows and a lattice of steel beyond. The bed was boxed into the floor so that he could not crawl under-neath; there was no provision by which he could hang himself: no hooks, brackets, electrical fixtures; even the door-hinges had sloping shoulders from which a cord or im-provised rope would slide.

A small group of psychiatrists examined Burke at length. He found them intelligent but either bluff and windy or vague and tentative, as if they groped through an eternal fog of obfuscation, which might have arisen either from the difficulty of their subject or the falsity of their basic premis-es. In their turn, the psychiatrists found Burke articulate and polite, though they could not help but resent his air of sad derision as they applied the various tests, charts, draw-ings, and games by which they hoped to measure the pre-cise degree of his abnormality.

In the end they failed. Burke's insanity refused to re-veal itself in any objective manner.

Nevertheless the psy-chiatrists concurred in an intuitive diagnosis: "extreme para-noia." They described him as "deceptively rational, his ob-sessions craftily veiled." So craftily veiled indeed was his abnormality (they pointed out) that only trained psycho-pathologists like themselves could have recognized it. They reported Burke to be listless and withdrawn, with little in-terest in anything except the condition and whereabouts of his victim, Dr. Ralph Tarbert, whom he made repeated re-quests to see—requests which, of course, were denied. They required a further period in which to study Burke before making a definite recommendation to the court.

The days went on and Burke's paranoia appeared to inten-sify. The psychiatrist noted symptoms of persecution. Burke gazed wildly around his chamber as if following floating shapes.

He refused to eat and grew thin; he feared the dark so strongly that a night light was allowed him.

On two occasions he was observed beating at the empty air with his hands.

Burke was suffering not only mentally but physically. He felt a constant tugging and twisting inside his brain—a sen-sation similar to his original denopalization, although mer-cifully less intense. The Xaxans had not warned him of these torments. If they were forced to submit to them once a month, in addition to the brilliant agonies of denopali-zation, Burke could sympathize with their determination to expunge the nopal from the universe.

The working at his mind grew ever more violent. He began to fear himself half-crazed in actuality. The psychia-trists propounded solemn questions, inspecting him owlishly, while the nopal riding in and out of the room on their shoulders watched with an almost equal degree of bland wisdom. The staff physician at last ordered sedation, but Burke resisted, fearing sleep. The nopal hung close above, staring into his eyes, the spines fluffing and jerking and spreading, like a chicken bathing in the sand. The physi-cian called orderlies, Burke was grasped, the needle shoved home, and in spite of his furious determination to stay awake, he lapsed into stupor.

Sixteen hours later he awoke, and lay listlessly gazing at the ceiling. His headache had gone, he felt sodden and stuffy, as if sick with a cold. Recollections came slowly, in re-luctant fragments. He raised his eyes, searched the air above his bed. No nopal could be seen—to his intense relief. He sighed, lay back on the pillow.

The door opened, an orderly wheeled in a cart with a tray of food.

Burke sat up, looked at the orderly. No nopal. The space over the man's head was vacant; no baleful orbs stared down across the white-jacketed shoulders.

A thought came to Burke; he hunched back down. Slow-ly he raised his hand, felt the back of his neck. Nothing but his own skin and the bristle of his own hair....

The orderly stood watching him. Burke seemed quieter, almost normal. The staff psychiatrist, making his rounds, re-ceived the same impression. He held a short conversation with Burke, and could not escape the conviction that Burke had returned to normal. He therefore kept a promise he had made a few days earlier and telephoned Margaret Ha-ven, informed her that she might visit Burke during the reg-ular visiting hours.

That same afternoon Burke was notified that Miss Mar-garet Haven had come to see him.

Burke followed the or-derly to the cheerful waiting room, so deceptively like the lobby of a country hotel.

Margaret ran across the room, seized his two hands. She searched his face, and her own face, wan and thin, lit up with happiness. "Paul! You're back to normal! I know! I can tell!"

"Yes," said Burke, "I'm my own self again." They sat down. "Where's Ralph Tarbert?" he asked.

Margaret's gaze wavered. "I don't know. He dropped out of sight as soon as he had left the hospital." She squeezed Burke's hands. "I'm not supposed to talk of things like that; the doctor doesn't want me to excite you."

"Considerate of him. How long do they plan to keep me here?"

"I don't know. Until they make up their minds about you, I suppose."

"Hmph. They can't keep me here forever, unless they get a formal commitment of some kind...."

Margaret turned her gaze aside. "As I understand it, the police have washed their hands of the case. Dr. Tarbert has refused to bring charges against you; he insists that you and he were conducting an experiment. The police think he's just as—" She stopped short.

Burke laughed shortly. "Just as crazy as I am, eh? Well, Tarbert's not crazy. It happens that he's telling the truth."

Margaret leaned forward, her face full of doubt and anx-iety. "What's going on, Paul? You're doing something strange —it's not just government work, I'm sure of that! And what-ever it is, it worries me!"

Burke sighed. "I don't know. . . . Things have changed. Perhaps I was crazy; perhaps I spent a month involved in the strangest conceivable delusion. I'm not sure."

Margaret looked away, and said in a low voice, "I've been wondering whether I acted correctly in calling the po-lice. I thought you were killing Dr. Tarbert. But now"— she made a small nervous gesture—"now I don't know."

Burke said nothing.

"You're not going to tell me?"

Burke grinned wanly, shook his head. "You'd think I was crazy for sure."

"You're not angry with me?"

"Of course not."

The bell signaling the end of visiting hours rang; Mar-garet rose to her feet. Burke kissed her, and noticed that her eyes were moist. He patted her shoulder. "Someday I'll tell you the whole story—perhaps as soon as I'm out of here."

"You promise, Paul?"

"Yes. I promise."

The next morning Dr. Kornberg, the institution's head psy-chiatrist, looked in on Burke during his routine weekly check. "Well, Mr. Burke," he asked bluffly, "how are you getting along?"

"Very well," said Burke. "In fact I'm wondering when I can be released."

The psychiatrist donned the quizzical noncommittal ex-pression with which he met this sort of question. "When we feel that we know what, if anything, is wrong with you. Frankly, Mr. Burke, you're a puzzling case."

"You're not convinced that I'm normal?"

"Ha ha! We can't make snap decisions merely on the ba-sis of impressions! Some of our most disturbed people ap-pear disarmingly normal. I don't refer to you, of course—al-though you still exhibit a few rather puzzling symptoms."

"Such as?"

The psychiatrist laughed. "That's giving away profession-al secrets. 'Symptoms' perhaps is too strong a word." He considered. "Well, let's face it man to man. Why do you study yourself in the mirror five minutes at a time?"

Burke grinned painfully. "Narcissism, I suppose."

The psychiatrist shook his head. "I doubt it. Why do you grope at the air over your head? What do you expect to find?"

Burke rubbed his chin thoughtfully. "You apparently caught me at a yoga exercise."

"I see." The psychiatrist hoisted himself to his feet. "Well, well."

"Just a minute, doctor," said Burke. "You don't believe me, you think me either facetious or craftily evasive; in either case, still paranoid. Let me ask you a question. Do you con-sider yourself a materialist?"

"I subscribe to none of the metaphysical religions, which includes—or excludes—them all, I suppose. Does that ans-wer your question?"

"Not entirely. What I'm after is this: Can you admit the possibility of events and experiences which are—well, out of the ordinary?"

"Yes," said Kornberg warily, "to a certain extent."

"And a man who had participated in one of these extra-ordinary events, and described it might well be considered insane?"

"Yes, certainly," said Kornberg. "However, if you notified me that you had recently seen a blue giraffe on roller skates playing a harmonica, I wouldn't believe you."

"No, because it would be an absurdity, a burlesque of normality." Burke hesitated. "I won't go any farther—since I want to get out, of here as soon as possible. But these actions you've observed—the looking into the mirror, feel-ing the air—all stem from circumstances which I regard as —well, remarkable."

Kornberg laughed. "You're certainly cautious."

"Naturally. I'm talking to a psychiatrist at the lunatic asylum, who already considers me aberrated."

Kornberg abruptly rose to his feet. "I've got to be on my rounds."

Burke took care not to examine himself in the mirror, not to feel the air over his shoulders. A week later he was re-leased from the asylum. All charges against him had been dropped; he was a free man.

Dr. Kornberg shook hands with him on his departure. "I'm curious as to the 'remarkable circumstances' you mentioned."

"I am, too," said Burke. "I'm going out now to investigate them. Perhaps you'll have me back before long."

Kornberg shook his head in wry admonition; Margaret took Burke's arm, led him to her car.

Here she hugged him, kissed him enthusiastically. "You're out! You're free, you're sane, you're—"

"Unemployed," said Burke. "Now I want to see Tarbert. Instantly."

Margaret's face, a water-clear mirror for her every emo-tion, displayed disapproval. She said with all-too-transpar-ent airiness, "Oh, let's not bother with Dr. Tarbert. He's busy with his own affairs."

"I've got to see Ralph Tarbert."

Margaret stammered uncertainly, "Don't you think—well, let's go somewhere else."

Burke smiled sardonically. Evidently Margaret had been instructed—or had decided for herself—that it would be best to steer Burke away from Tarbert.

"Margaret," he said softly, "you're fooling with something you don't understand. I've got to see Tarbert."

Margaret cried in distress, "I don't want you to be in-volved again . . . Suppose you—well, get all excited again!"

"I'll get much more excited if I don't see Tarbert. Please, Margaret. Today I'll explain everything."

"It's not only you," said Margaret miserably. "It's Dr. Tarbert. He's changed! He was so—well, civilized, and now he's savage and bitter. Actually, Paul, I'm afraid of him. He seems evil!"

"I'm sure he isn't. I've got to see him."

"You promised to tell me how you got in that terrible situation."

"So I did." Burke heaved a deep sigh. "I'd like to keep you uninvolved as long as possible. But I promised and— let's go see Tarbert. Where is he?"

"At Electrodyne Engineering. He moved in when you left. He's become very queer."

"I don't wonder," said Burke. "If all this is real—if I'm not a real maniac—"

"Don't you know?"

"No," said Burke. "I'll find out from Tarbert. I hope I'm crazy. I'd be relieved and happy if I could believe I were."

Margaret's face showed her shock and bewilderment; nev-ertheless, she said no more.

They drove slowly out Leghorn Road, Margaret's reluc-tance to proceed becoming ever more marked. And Burke himself began to find reasons why visiting Tarbert was a poor idea. His brain flashed with crackles of pale light, sounded to a sibilant hiss, and there was a sensation almost like a thud in his auditory centers. A thud, a growl. "Gher —gher—gher—" the sound he had heard before, on Ixax. Or was Ixax an illusion, and he himself insane? Burke fret-fully shook his head.

The whole affair was insane. Impelled by some wild delusion he'd tied poor Tarbert to his home-made torture machine and no doubt nearly killed him. Tar-bert might be difficult, even unpleasant. . . . He definitely had no wish to see Tarbert. The closer they approached Electrodyne Engineering, the stronger grew his reluctance, and the louder grew the grating sound in his mind:

"Gher —gher—gher." The glimmer of light in his brain increased in intensity, swam before his eyes like visions. He saw bloom-ing dark colors, an object repellently like a drowned woman floating deep in a black-green ocean, her long pale hair float-ing free. . . . He saw waxy sea-weed crusted with colored stars, like blossoms on a hollyhock. He saw a vat of churn-ing spaghetti the strands drawn from quaking blue-green glass. . . . Burke drew in his breath with a hiss, wiped his eyes with the back of his hand.

Margaret looked hopefully toward him with each of his uneasy movements—but Burke clamped his mouth obstinate-ly. When he saw Tarbert he'd know the truth. Tarbert would know.

Margaret drove into the parking lot. There was Tarbert's car. On leaden feet Burke walked toward the door to the office. The growl inside his brain was absolutely menacing. Within the building lurked an evil presence; it was as if Burke were a prehistoric man in front of a dark cave which smelled of blood and carrion. . . .

He tried the door to the office; it was locked. He knock-ed.

Somewhere within a presence stirred. Flee while there's still time! Still time! Still time! Don't wait! Don't wait! Too late! Don't wait! Still time!

Tarbert appeared in the doorway—a bloated monstrous Tarbert, a vile malevolent Tarbert.

"Hello, Paul," he sneered. "They finally let you out?"

"Yes," said Burke in a voice he could not keep from trem-bling. "Ralph, am I crazy—or not?

Can you see it?"

Tarbert looked at him with the cunning of a hungry shark. He meant to trap Burke, to involve him in mis-fortune and tragedy.

"It's there."

Burke's breath rasped out through his constricted throat. Margaret's frightened voice came from behind him. "What's there? Tell me, Paul! What is it?"

"The nopal," croaked Burke. "It's sitting on my head, sucking at my mind."

"No!" said Margaret, taking his arm. "Look at me, Paul! Don't believe Tarbert! He's lying!

There's nothing there! I can see you, and there's nothing there!"

"I'm not crazy," said Burke. "You can't see it because you've got one too. It won't let you see. It tries to make us believe Ralph is vicious—just as it made you think I was."

Margaret's face sagged in shock and incredulity. "I didn't want to involve you," said Burke, "but since you are, you might as well know what's going on."

"What is a 'nopal'?" whispered Margaret.

"Yes," said Tarbert hollowly, "what is a nopal? I don't know either."

Burke took Margaret's arm, led her into the office. "Sit down." Margaret gingerly took a seat; Tarbert leaned against the counter. "Whatever the nopal is," said Burke, "it's not nice. Evil spirit, familiar, mind-parasite—these are just names; they don't describe the things. But they're able to influence us. Right now, Margaret, they're telling us to hate Tarbert. I never realized how powerful the things are until I turned down Leghorn Road."

Margaret raised her hands to her head. "It's on me now?"

Tarbert nodded. "I can see it. It's not pretty."

Margaret slumped into a chair, hands twisting in her lap. She turned Burke an uncertain white-faced grin. "You're joking, aren't you? Just trying to scare me?"

Burke patted her hand. "I wish I were. But I'm not."

Margaret said, still unbelieving, "But why haven't other people seen them? Why aren't they known to scientists?"

"I'll tell you the whole story."

"Yes," said Tarbert dryly. "I'll be interested to hear it. I know absolutely nothing except that everyone carries a mon-ster riding on their heads."

"Sorry, Ralph," said Burke, grinning. "I imagine it came as something of a shock?"

Tarbert nodded grimly. "You'll never know."

"Well, here's the story . . ."

X

evening had come; the three sat in the workshop, in a pool of light around the denopalizer. On the workbench an electric percolator bubbled.

"It's a cruel situation," said Burke. "Not only for us, but for everyone. I had to have help, Ralph. I had to drag you into it."

Tarbert sat staring at the denopalizer. There was silence in the room, except for the chanted growling sound in Burke's mind. Tarbert still seemed the embodiment of all danger and evil, but Burke, closing his mind to the idea, insisted that Tarbert was his friend and ally—even though he could not look into Tarbert's malevolent countenance.

Burke stirred himself. "You still have a choice. After all, this is not your responsibility—not mine either for that mat-ter. But now that you know what's going on, you can still pull out if you like, and no hard feelings."

Tarbert grinned sadly. "I'm not complaining. Sooner or later I'd have been involved. I'd just as soon be in at the beginning."

"So would I," said Burke with relief. "How long was I in the asylum?"

"About two weeks."

"In about another two weeks the nopal will drop down on you. You'll go to sleep, you'll wake up thinking it was all a terrible nightmare. That's how I felt. You'll have no trouble forgetting it, because the nopal will help you for-get."

Tarbert's eyes focused on a spot above Burke's shoulder. He shivered. "With that thing looking at me?" He shook his head. "I don't understand how you can bear hosting it, knowing what it is."

Burke grimaced. "It's doing its best to smother the re-vulsion. . . . They choke away ideas they don't like—achieve a certain degree of control. They can encourage the hos-tilities latent in everybody; it's dangerous to be Tauptu in a world of Chitumih."

Margaret stirred uneasily. "I don't understand what you hope to do."

"It's not what we hope to do—it's what we must do. The Xaxans have given us an ultimatum: Clean up our planet, or they'll clean it for us. They have the capabilities; they're ruthless enough."

"I can sympathize with their determination," Tarbert said thoughtfully. "They've apparently suffered a great deal."

"But they're inflicting, or trying to inflict, this same suf-fering on us!" protested Burke. "I find them callous, harsh, domineering—"

"You saw them under the worst possible circumstances," Tarbert pointed out. "They seemed to treat you as polite-ly as possible. My impulse is to defer judgment on the Xaxans, until we know them better."

"I know them well enough now," growled Burke. "Don't forget, I was witness to—" He stopped short. The nopal presumably were urging him to attack the Xaxans. Tarbert's defense was probably the rational attitude. . . . Still, on the other hand . . . Tarbert interrupted his speculations.

"There's a great deal I don't understand," he said. "For in-stance, they call Earth, Nopalgarth; they want us to purge ourselves of nopal, ostensibly to cure a pest-hole condition. But the universe is very large and there must be many other worlds plagued by nopal. They can't expect to tidy up the entire universe! You can't eradicate mosquitoes by spraying one pool in a swamp."

"According to what I was told," said Burke, "this is precisely their aim. They're conducting an anti-nopal cru-sade, and we're the first converts. So far as Earth is con-cerned, it's up to us.

We've got a tremendous responsibility —and I don't see how we're going to discharge it."

"But surely," Margaret said uncertainly, "if these things exist, and you told people—"

"Who'd believe us? We can't just start denopalizing each casual passer-by; we'd last about four hours. If we went to some remote island and set up a colony of Tauptu, and if by some chance we escaped persecution and extermina-tion, we'd eventually touch off a Xaxan-type war."

"Then—" Margaret started, but Burke interrupted her: "If we do nothing, the Xaxans will destroy us. They've destroyed millions of Chitumih on Ixax; why should they hes-itate to do the same here?"

"We must compose ourselves to quiet reflection," said Tarbert. "I can think of a dozen questions I'd like to ex-plore. Is there any way to expunge these damnable nopal other than the torture machine? Is it possible that the nopal are merely a part of the human organism, such as the so-called soul, or some kind of refracted image of the mental processes? Or possibly of the unconscious mind?"

"If they're part of ourselves," Burke pondered, "Why should they seem so hideous?"

Tarbert laughed. "If I dangled your intestines in front of your face, you'd find them revolting enough."

"True," said Burke. He considered a moment. "In response to your first question: The Xaxans know of no way to purge the Chitumih except by the denopalizer. This of course does not mean that no other way exists. As for nopal being part of the human, organism, they certainly don't act like it. They float around hungrily, they cross to other planets, they act like independent creatures.

If some kind of man-nopal symbiosis is involved, it seems all to the benefit of the nopal. So far as I know they confer no advantages upon their host—although I know of no active harm they do either."

"Then why are the Xaxans so all-fired anxious to be rid of them, to cleanse the universe of the nopal?"

"Because they're disgusting, I suppose," said Burke. "That seems reason enough for them."

Margaret shivered. "There must be something wrong with me. ... If these things exist, and you both say they do, I should feel more of this disgust—but I don't. I'm just numb."

"Your nopal clamps down on the proper nerve at the proper time," said Burke.

"This fact," said Tarbert, "would imply that the nopal pos-sesses a considerable intelligence—and sets up a new collec-tion of questions: Does the nopal understand words, or merely feel raw emotion? Apparently it lives upon a single host until the host dies, in which case it has opportunity to learn the language. But, on the other hand, it may not pos-sess that large a memory-bank. Possibly no memory at all."

Margaret said, "If it stays on a person until a person dies, then it's to the nopal's advantage to keep that person alive."

"So it would seem."

"This might account for premonitions of danger, hunches, and things like that."

"Very possibly," said Tarbert. "It's one of the ideas we certainly would want to explore."

There was peremptory knocking at the outside door. Tar-bert rose to his feet; Margaret twisted around startled, hand to her mouth.

Tarbert slowly started for the door; Burke stopped him. "Let me go. I'm Chitumih, like everyone else."

He started across the dim workshop, toward the office and the outer door. Halfway he stopped.

He looked back. Margaret and Tarbert, in the little island of yellow light, stood immobile, waiting and watching.

He slowly turned, fighting against a fearful reluctance he had come to recognize.

The rap-rap-rap sounded again, a measured ominous sound.

Burke forced his laggard legs into motion, pushed him-self through the dark office, past the long counter, to the door.

He looked out through the glass panel, strained to see into the night. The dim half-moon hung behind a tall cy-press tree; in a shadow stood a massive dark shape.

Burke slowly opened the door. The figure stalked for-ward; the flash of headlights from cars passing along Leg-horn Road revealed rough gray skin, a jutting ridge of nose like a bent bow, opaque eyes: Pttdu Apiptix, the Xaxan. Be-hind, in the darkness, more sensed than seen, loomed four other Xaxan shapes. All wore black beetle-shell cloaks and metal helmets with spikes along the ridge.

Apiptix gazed stonily down at Burke. All the hate and fear Burke had originally felt for the Tauptu surged back. He resisted; he thought of his nopal peering at the Xaxans across his shoulders, but to no avail.

Pttdu Apiptix came slowly forward—but now out on the highway a hundred feet away an automobile braked to a halt. A red light began blinking, a search-light swung to-ward the Electrodyne plant.

Burke jumped forward. "Behind the trees, quick! The Highway Patrol!"

The Xaxans moved into the shadow, to stand like a row of barbaric statues. From the patrol car came the sound of radio voices, then the door opened and two figures alighted.

Heart in throat Burke stepped forward. A flashlight played on his face. "What's the trouble?" he asked.

There was no reply for a moment; nothing but a sus-picious scrutiny. Then the trooper's cool voice: "Nothing's the trouble; we're just making a check. Who's inside the plant?"

"Friends."

"You have authority to use this place?"

"Certainly."

"Mind if we take a look around?" They advanced, not caring whether Burke minded or not. Their flash-lights turn-ed here and there, never straying too far from Burke.

"What are you looking for?" Burke asked.

"Nothing in particular. Something's wrong about this place, something fishy going on. There's been trouble here before."

With heart in mouth Burke watched their progress. Twice he started to call a warning; twice his voice caught in his throat. What could he tell them? They were oppressed by the nearness of the Xaxans; there was nervousness in the flick of their lights. Burke could see the shapes under the trees; the lights strayed toward them. . . . Margaret and Tarbert appeared in the doorway. "Who is it?" called Tarbert.

"Highway Patrol," said one of the troopers. "Who are you?"

Tarbert told them. After a moment the patrolmen turned back toward the highway. One of the flashlight beams play-ed into the shadow of the cypress trees. The light hesitated, steadied. The patrolmen gasped. Their revolvers jerked out into their hands. "Come out of there—whoever you are!"

For answer there were two puffs of pink flame, two twinkling pink lines. The patrolmen flared, tumbled back, collapsed like empty sacks.

Burke cried out, stumbled forward, stopped short. Pttdu Apiptix looked at him briefly, then turned to the door. "Let us go in," said the voice-box.

"But these men!" croaked Burke. "You've murdered them!"

"Calm yourself. The corpses will be removed; the auto-mobile also."

Burke looked toward the patrol car, now sounding to the metallic sound of the dispatcher's voice.

"You don't seem to understand what you've done! We can all be arrested, executed . . ." His voice died as he rea-lized the nonsense he was talking. Apiptix, ignoring him, walked into the building with two of his fellows at his heels. The remaining two turned back toward the corpses.

Burke shrank back with a crawling skin; Tarbert and Margaret retreated before the stalking gray shapes.

The Xaxans halted at the edge of the pool of light; Burke spoke to Tarbert and Margaret in a bitter voice. "If you harbored any lurking doubts—"

Tarbert nodded shortly. "I've discarded them."

Apiptix approached the denopalizer, examined it without comment. He turned to Burke, "This man"—he indicated Tar-bert—"is the single Tauptu on Earth. In the time availa-ble you might have organized an entire squadron."

"I've been locked up," said Burke in a surly tone. The hate he felt for Pttdu Apiptix—could it be completely nopal-inspired? "Also, I'm not sure that denopalizing a large num-ber of persons is the best thing to do."

"What else do you propose?"

Tarbert spoke soothingly. "We feel that we must learn more about the nopal. Perhaps there are easier ways to denopalize." He scrutinized the Xaxans with bright interest. "Have you yourselves tried other means?"

Apiptix's mud-colored eyes felt impassively over Tarbert. "We are warriors, not savants. The nopal of Nopalgarth come to Ixax; once a month we burn them away from our minds. They are your pests. You must take immediate steps against them."

Tarbert nodded—with rather too easy an acquiescence, thought Burke resentfully. "We agree that you have cause for impatience."

"We need time!" Burke exclaimed. "Surely you can spare us a month or two!"

"Why do you need time? The denopalizer is ready! Now you must use it!"

"There is such an enormous amount to be learned!" cried Burke. "What are the nopal? No one knows. They seem repulsive, but who knows? Perhaps they even exert a bene-ficial effect!"

"An amusing speculation." Apiptix appeared anything but amused. "I assure you that the nopal are harmful; they have harmed Ixax by causing a war of a hundred years."

"Are the nopal intelligent?" Burke continued. "Can they communicate with men? These are things we want to know."

Apiptix regarded him with what seemed to be amaze-ment. "From where do you derive these ideas?"

"Sometimes I think the nopal is trying to tell me some-thing."

"To what effect?"

"I'm not sure. When I come close to a Tauptu there's an odd sound in my mind: something like gher, gher, gher."

Apiptix slowly turned his head, as if not trusting him-self to look at Burke.

Tarbert said, "It's true that we know very little. Re-member, our tradition is to learn first, then act."

"What is nopal-cloth?" asked Burke. "Can it be made from anything beside the nopal? And something else which puz-zles me—where did the first piece of nopal-cloth come from? If a single man were accidentally denopalized, it's hard to see how he could have personally fabricated the cloth."

"These are irrelevances," said the Xaxan voice-box.

"Perhaps, perhaps not," said Burke. "They indicate an area of ignorance, which may exist for both of us. For in-stance, do you know how the first piece of nopal-cloth came into existence, and how?"

The Xaxan stared at him a moment, his beer-colored eyes blank. Burke was unable to read his emotions. Finally the Xaxan said, "The knowledge, if it exists, can not help you destroy the nopal.

Proceed then in accordance with your directions."

The voice, though flat and mechanical, still managed to convey sinister overtones. But Burke, summoning all his courage, persisted: "We just can't act blindly. There's too much we don't know.

This machine destroys the nopal, but it can't be the best method, or even the best approach to the problem! Look at your own planet: in ruins; your people: almost wiped out! Would you want to inflict the same disaster on Earth? Give us a little time to learn, to experiment, to get a grip on the subject!"

For a moment the Xaxan held to silence. Then the voice-box said, "You Earthmen are over-ripe with subtlety. For us the destruction of nopal is the basic and single issue. Re-member, we do not need your help; we can destroy the nopal of Nopalgarth at any time: tonight, tomorrow. Do you wish to know how we will do this, if necessary?" With-out waiting for answer he stalked to the table, lifted the scrap of nopal-cloth. "You have used this material, you know its peculiar qualities.

You know that it is without mass and inertia, that it responds to telekinesis, that it is almost infinitely extensible, that it is impenetrable to the nopal."

"So we understand."

"If necessary, we are prepared to envelope Earth in a swath of nopal-cloth. We can do this.

The nopal will be trapped and as Earth moves they will be pulled away from the brains of their hosts. The brains will hemorrhage and people of Earth will die."

No one spoke. Apiptix continued. "This is a drastic re-course—but we will be tormented no longer. I have ex-plained what must be done. Exterminate your nopal, or we will do so ourselves."

He turned away, and with his two comrades, crossed the workshop.

Burke followed, burning with indignation. Trying to keep his voice calm, he said to the tall black-cloaked backs: "You can't expect us to perform miracles! We need time!"

Apiptix did not slow his pace. "You have one week". He and his fellows passed out into the night. Burke and Tarbert followed. The two who had remained outside appeared from the shadow of the cypress trees, but the corpses and the patrol car were nowhere to be seen. Burke tried to speak, but his throat tightened and the words refused to come. As he and Tarbert watched, the Xaxans stood stiffly, then rose into the night, accelerating, blurring, disappearing into the spaces between the stars.

"How in the world do they do that?" Tarbert asked in wonder.

"I don't know." Nauseated and limp Burke sank down upon a step.

"Marvelous!" Tarbert said. "A dynamic people—they make us seem like clams."

Burke gazed at him with suspicion. "Dynamic and mur-derous," he said sourly. "They've mixed us a pot of trouble. This place will be swarming with police."

"I don't think so," said Tarbert. "The bodies, the car, are gone. It's an unfortunate affair—"

"Especially for the cops."

"You've got nopal trouble," Tarbert remarked, and Burke forced himself to believe that Tarbert was right. He rose to his feet; they returned inside.

Margaret waited in the outer office. "Are they gone?"

Burke nodded curtly. "They're gone."

Margaret shuddered. "I've never been so afraid in my life. It's like swimming and seeing a shark come toward you."

"Your nopal is twisting things," said Burke hollowly. "I can't think straight either." He looked at the denopalizer. "I suppose I should take the treatment." His head suddenly be-gan to throb with pain. "The nopal doesn't think so." He sat down, closed his eyes. The ache slowly diminished.

"I'm not so sure it's a good idea," said Tarbert. "You'd better keep your nopal for awhile. One of us has to en-list recruits for the squadron—as the Xaxan puts it."

"Then what?" asked Burke in a muffled voice. "Tommy-guns? Molotov cocktails? Bombs? Who do we fight first?"

"It's so brutal and senseless!" Margaret protested fiercely.

Burke agreed. "It's a brutal situation—and we can't do much about it. They allow us no freedom of action."

"They've spent a century fighting these things," Tarbert argued. "They probably know all there is to know about the nopal."

Burke sat up in outrage. "Good heavens no! They ad-mit they know nothing! They're pushing us, trying to keep us off-balance. Why? A few days more or less—what's the difference? There's something peculiar going on!"

"Nopal-talk. The Xaxans are harsh, but they seem honest. Apparently they aren't as ruthless as the nopal would have you think. Otherwise they'd denopalize Earth at once with-out giving us the chance to do it ourselves."

Burke tried to order his thoughts.

"Either that," he said presently, "or they have another reason for wanting Earth denopalized but populated."

"What reason could they have?" asked Margaret.

Tarbert shook his head skeptically. "We're becoming over-ripe again, as the Xaxans would say."

"They allow us no time whatever for research," said Burke. "Personally I don't want to embark on a project as big as this without studying it. It's only reasonable that they give us a few months."

"We've got a week," said Tarbert.

"A week!" snarled Burke. He kicked the denopalizer. "If they'd allow us to work up something different, something easy and painless, we'd all be better off." He poured a cup of coffee, tasted it, spat in disgust. "It's been boiling."

"I'll make fresh," Margaret said hurriedly.

"We've got a week," said Tarbert, pacing with hands be-hind his back. "A week to conceive, explore and develop a new science."

"Nothing to it," said Burke. "It's only necessary to fix on a method of approach, invent tools and research techniques, work up nomenclatures. Then it's duck soup. We merely concentrate on the specific application: the swift denopaliza-tion of Nopalgarth. After sorting through and testing our ideas, we can take the rest of the week off."

"Well, to work," Tarbert said dryly. "Our starting point is the fact that the nopal exist. I'm watching your private nopal, and I can see that it doesn't like me."

Burke squirmed fretfully, aware—or at least imagining him-self aware—of the entity on his neck.

"Don't remind us," said Margaret, returning with the percolator. "It's bad enough simply knowing."

"Sorry," said Tarbert. "So we start with the nopal, crea-tures completely outside our old scheme of things. The simple fact of their existence is meaningful. What are they? Ghosts?

Spirits? Demons?"

"What difference does it make?" growled Burke. "Class-ifying them doesn't explain them."

Tarbert paid him no heed. "Whatever they are, they're built of stuff foreign to us: a new kind of matter, only semi-visible, impalpable, without mass or inertia. They seem to draw nourishment from the mind, from the process of thought, and their dead bodies respond to telekinesis, a most sugges-tive situation."

"It suggests that thought is a process rather more sub-stantial than we've heretofore believed,"

said Burke. "Or perhaps I should say that there seem to be substantial pro-cesses going on, which relate to thought in some manner we can't yet define."

"Telepathy, clairvoyance, and the like—the so-called psion-ic phenomena—indicate the same, of course," mused Tar-bert. "It's possible that nopal-stuff is the operative material. When something—a thought or a vivid impression—passes from one mind to another, the minds are physically linked —somehow, in some degree. Action at a distance can't be allowed. In order to know the nopal, we might well concern ourselves with thought."

Burke wearily shook his head. "We know no more about thought than we do about the nopal.

Even less. Encephalo-graphs record a by-product of thought. Surgeons report that certain parts of the brain are associated with certain kinds of thought. We suspect that telepathy occurs instantaneous-ly, if no faster—"

"How could anything be faster than instantaneous?" Mar-garet inquired.

"It could arrive before it started. In which case it's called precognition."

"Oh."

"In any event it seems that thought is a different stuff from our usual matter, that it obeys different laws, acts through a different medium, in a different dimension-set, in short, works through a different space—implying a differ-ent universe."

Tarbert frowned. "You're getting a little carried away; you're using the word 'thought' rather too easily. After all, what is 'thought? So far as we know, it's a word to describe a complex of electrical and chemical processes in our brains, these more elaborate, but intrinsically no more mysterious, than the operation of a computer. With all the good will and predisposition in the world, I can't see how 'thought' can work metaphysical miracles."

"In this case," said Burke, somewhat tartly, "what do you suggest?"

"Just for a starter, some recent speculations in the field of nuclear physics. You're naturally aware how the neutrino was discovered: more energy went into a reaction then came out of it, suggesting that an undiscovered particle was at work.

"Well, new, rather more subtle, discrepancies have shown themselves: Parities and indexes of strangeness don't come out quite right, and it seems that there's a new and unsus-pected 'weak'

force at work."

"Where does all this take us?" demanded Burke, then forced himself to erase his exasperated frown and replace it with a somewhat pallid smile. "Sorry."

Tarbert made an unworried gesture. "I'm watching your nopal. . . . Where does all this take us?

We know of two strong forces: nuclear-binding energy, electro-magnetic fields; and—if we ignore the beta decay force—one weak force: gravity. The fourth force is far weaker than gravity, even less perceptible than the neutrino. The implications seem to be—or at least, may be—that the universe has a shadow counterpart, completely congruent, based upon this fourth force. It's still all one universe naturally and there's no ques-tion of new dimensions or anything bizarre. Just that the material universe has at least another aspect composed of a substance, or field, or structure—whatever you want to call it—invisible to our senses and sensor mechanisms."

"I've read something of this in one of the journals," said Burke. "At the time I didn't pay too much attention. . . . I'm sure you're on the right track. This weak-force universe, or para-cosmos, must be the environment of the nopal, as well as the domain of psionic phenomena."

Margaret was moved to exclaim. "But you insisted that this fourth-force 'para-cosmos' is undetectable! If telepathy isn't detectable, how do we know it exists?"

Tarbert laughed. "A lot of people say it doesn't exist. They haven't seen the nopal." He turned a wry glance at the space over Burke's and Margaret's heads. "The fact is that the para-cosmos is not quite undetectable. If it were, the dis-crepancies by which the fourth force has been discovered would never have been noticed."

"Assuming all this," said Burke, "and of course we've got to assume something, it appears that the fourth force, if sufficiently concentrated, can influence matter. More accurate-ly, the fourth force influences matter, but only when the force is intensely concentrated do we notice the effect."

Margaret was puzzled. "Telepathy is a projection or a beam of this 'fourth force'?"

"No," said Tarbert. "I wouldn't think so. Remember, our brains can't generate the 'fourth force.' I don't think we need to stray too far from conventional physics to explain psionic events—once we assume the existence of an analogue universe, congruent to our own."

"I still don't see it," said Margaret. "And isn't telepathy supposed to be instantaneous? If the analogue world is ex-actly congruent to our own, why shouldn't events take place at the same speed?"

"Well—" Tarbert considered a few minutes. "Here's some more hypothesis—or I'll even call it

'induction.' What we know of telepathy and the nopal suggests that the analogue particles enjoy considerably greater freedom than our own —balloons compared to bricks. They're constructed of very weak fields, and also, much more importantly, aren't con-strained to rigidity by the strong fields. In other words, the analogue world is topologically congruent to our own but not dimensionally. In fact, dimensions have no real mean-ing."

"If so, 'velocity' is also a meaningless word, and 'time' as well," said Burke. "This may give us a hint as to the theory of the Xaxan space-ships. Do you think it's possible that somehow they enter the analogue universe?" He held up his hand as Tarbert started to speak. "I know—they're already in the analogue universe. We mustn't confuse our-selves with fourth-dimensional concepts."

"Correct," said Tarbert. "But back to the linkage between the universes. I like the balloon-brick image. Each balloon is tied to a brick. The bricks can disturb the balloons, but vice-versa, not so easily. Let's consider how it works in the case of telepathy. Currents in my mind generate a corres-ponding flow in the para-cosmos analogue of my mind— my shadow-mind, so to speak.

This is a case of the bricks jerking the balloons. By some unknown mechanism, maybe by my analogue self creating analogue vibrations which are interpreted by another analogue personality, the balloons jerk the bricks; the neural currents are transferred back to the receiving brain. If conditions are right."

"These 'conditions,' " said Burke sourly, "may very well be the nopal."

"True. The nopal apparently are creatures of the para-cosmos, constructed of balloon-stuff, and for some reason viable in either of the universes."

The coffee had percolated; Margaret poured. "I wonder," she asked, "if possibly the nopal have no existence in this universe whatever?"

Tarbert raised his eyebrows in pained protest—a demon-stration Burke thought rather exaggerated. "But I can see them!"

"Perhaps you only think you do. Suppose the nopal exis-ted only in the other cosmos, and preyed only on the ana-logues? You see them by clairvoyance, or rather, your ana-logue sees them—and it's so clear and vivid you think the nopal are real material objects."

"But my dear young lady—"

Burke interrupted. "It's quite sensible. I saw the nopal too; I know how real they appear. But they neither reflect nor radiate light. If they did, they'd appear on photographs. I don't believe they do have any base-world reality whatever."

Tarbert shrugged. "If they can prevent us from recognizing them in the natural state, they could do the same for photo-graphs."

"In many cases photographs are scanned by mechanical means. Irregularities could not help but show up."

Tarbert glanced at the air beside Burke's shoulder. "If you're right, why aren't the Xaxans aware of the situation?"

"They admit they know nothing of the nopal."

"They could hardly ignore something so basic," argued Tarbert. "The Xaxans are scarcely naive."

"I'm not so sure. Tonight Pttdu Apiptix acted unreason-ably. Unless . . ."

"Unless what?" asked Tarbert with, what Burke con-sidered, undue sharpness.

"Unless the Xaxans have some sort of ulterior motive. That's what I was about to say. I know it's ridiculous. I saw their planet; I know what they've suffered."

"There's certainly a great deal we don't understand," Tar-bert admitted.

"I'd breath a lot easier if a nopal weren't actually rest-ing on my actual neck," said Margaret. "If it's only haras-sing my analogue—"

Tarbert leaned quickly forward. "Your analogue is part of you, don't forget. You don't see your liver, but it's there and functioning. Just so your analogue."

"You agree that Margaret may be right?" asked Burke cautiously. "That the nopal actually is confined to the para-cosmos?"

"Well, it's as good a guess as any other," said Tarbert grudgingly. "I can think of two arguments counter. First the nopal-cloth, which I move with these, my own personal hands. Second, the control exerted by the nopal over our emotions and perceptions."

Burke jumped to his feet, paced back and forth. "The nopal might exert its influence through the analogue, so that when I think I'm touching nopal-cloth I'm only grasping air, that it's really the analogue who does the work—in fact, this is implication of the previous theory."

"In this case," said Tarbert, "Why can't I visualize my-self chopping up nopal with an imaginary axe?"

Burke felt a twinge of alarm. "No reason at all, I sup-pose."

Tarbert appraised the wisp of nopal-cloth. "No mass, no inertia—at least not in the base universe. If my telekine-tic powers are up to it I should be able to manipulate this nopal-stuff." The film rose limply into the air. Burke watched in revulsion. Disgusting stuff. It made him think of corpses, corruption, death.

Tarbert turned his head sharply. "Are you resisting me?"

Tarbert's arrogance, never his most endearing quality, was becoming intolerable, thought Burke. He started to say as much, then noting the malicious amusement in Tar-bert's eyes, clamped his mouth shut. He glanced at Margar-et, to find her watching Tarbert with a loathing equal to his own. The two of them perhaps might be able to ...

Burke caught himself up short, appalled by the direction of his thoughts. The nopal had infected him, this was only too clear. On the other hand—why should not a man have an idea of his own?

Tarbert had become twisted and male-volent; sheer dispassionate judgment could discern as much. Tarbert was tool to the alien creatures, not Burke! Tarbert and the Xaxans—enemies to Earth! Burke must counter them, or everyone would be destroyed. . . . Burke watched vigilantly as Tarbert concentrated on the nopal-cloth. The smoky wisp shifted, changed shape slowly, reluctantly.

Tarbert laughed rather nervously. "It's hard work. In the para-cosmos the stuff is probably fairly rigid. . . . Care to try?"

"No," said Burke in a throaty voice.

"Nopal-trouble?"

Burke wondered why Tarbert jeered so offensively.

Tarbert said, "Your nopal is excited. Its plumes are flut-tering and flickering. . . ."

"Why pick on the nopal?" Burke heard himself saying. "Other things are happening."

Tarbert gave him a sidelong glance. "That's a curious thing to say."

Burke halted in his pacing, rubbed his face. "Yes. Now that you mention it."

"Did the nopal put the words in your mouth?"

"No . . ." But Burke was not completely certain. "I had an intuition, something of the sort. The nopal probably was responsible. It gave me a quick glimpse of—something."

" 'Something'? Such as?"

"I don't know. I don't even remember it."

"Hmmph," said Tarbert. He turned his attention back once more to the wad of nopal-cloth, causing it to rise, fall, twist and spin. Suddenly he sent it darting twenty feet across the room, then gave a hideous laugh. "I've just bat-tered hell out of a nopal." He looked speculatively at Burke, turned his gaze over Burke's head.

Burke found himself on his feet, lurching slowly toward Tarbert. In his brain sounded the guttural now-familiar vocable: gher gher gher . . .

Tarbert drew back. "Don't let the thing dominate you, Paul. It's afraid, it's desperate."

Burke halted.

"If you don't beat it we've lost our fight—before we've even started." Tarbert looked from Burke to Margaret. "Neither of you hate me. Your nopal fear me."

Burke looked at Margaret. Her face was tight and strained. Her eyes met his.

Burke took a deep breath. "You're right," he said hus-kily. "You've got to be right." He returned to his seat. "And I've got to restrain myself. Your playing with that nopal-stuff does something to me, you'll never know. . .."

"Don't forget that I was 'Chitumih' myself once," said Tar-bert, "and I had to put up with you."

"You're hardly tactful."

Tarbert grinned, turned his attention back to the wad of nopal-stuff. "This is an interesting process. If I work hard I can wad it up. . . . I suppose that given enough time I could wipe out much of the nopal population. . . ."

Burke, seating himself, watched Tarbert with a stony gaze. After a moment he forced himself to relax. With the easing of taut muscles came the knowledge that he was very tired.

Tarbert said thoughtfully, "Now I'll try something else. I form two pads of nopal-stuff, I catch a nopal between; I squeeze. . . . There's resistance; then the thing collapses. Like cracking a walnut."

Burke winced. Tarbert looked at him with interest. "Cer-tainly you don't feel that?"

"Not directly."

Tarbert mused. "It's nothing to do with your own nopal."

"No," said Burke drearily. "It's just a twinge—induced fear—" He lacked both interest and energy to continue. "What time is it?"

"Almost three o'clock," said Margaret. She looked longing-ly toward the door. Like Burke she felt limp and drawn. How wonderful to be home in bed, indifferent to the nopal and all these strange problems. . . .

Tarbert, absorbed in his game of nopal-smashing, seemed fresh as the morning sun. A nauseous business, thought Burke. Tarbert was like an unpleasant urchin catching flies ....

Tarbert glanced at him, frowning, and Burke sat up in his chair, aware of a new tension. From a state of listless disapproval, he had begun to take a gradually more active interest in the game, and now found himself resisting Tar-bert's manipulations of the nopal-stuff with all his will. He was committed; hostility became overt between the two men. Beads of sweat started from Burke's forehead; his eyeballs thrust from their sockets. Tarbert sat rigid, face pinched and white as a skull. The nopal-stuff quivered; wisps and torn fragments wavered back and forth, into and away from the parent substance.

An idea came to Burke's mind, grew into conviction: this was more than an idle contest—much more! Happiness, peace, survival—all, everything, depended on the outcome. Holding the nopal-stuff rigid was not enough; he must wield it, slash at Tarbert, cut the vital cord, the umbilicus. . . . The nopal-stuff streamed and shifted to Burke's fervor, edged toward Tarbert.

Something new occurred, something unfore-seen and frightening. Tarbert ballooned with mental ener-gy. The nopal-stuff was whisked from Burke's mental-grip, flung far out of his control.

The game was at an end; likewise the contest of wills. Burke and Tarbert looked at each other, startled and be-mused. "What happened?" asked Burke in a strained voice.

"I don't know." Tarbert rubbed his forehead. "Some-thing came over me. ... I felt like a giant—irresistible." He laughed wanly. "It was quite a sensation. . . ."

There was silence for a moment. Then Burke said in a shaky voice, "Ralph, I can't trust myself; I've got to get rid of this nopal. Before it makes me do something—bad."

Tarbert considered for another long minute. "Perhaps you're right," he said at last. "If we're constantly at odd's-ends, we'll accomplish nothing." He rose slowly to his feet. "Very well, I'll denopalize you. If Margaret can put up with two fiends incarnate instead of just one." He chuckled feeb-ly.

"I can stand it. If it's necessary." And she muttered, "I suppose it is. ... I hope it is. In fact, I know it must be."

"Let's get it over with." Burke stood up, forced himself toward the denopalizer. The rage and reluctance of the no-pal pressed at him, sapped the strength off his muscles.

Tarbert looked sourly at Margaret. "You'd better go."

She shook her head. "Please let me stay."

Tarbert shrugged; Burke was too weary to insist. A step toward the denopalizer, another step, a third—it was like walking through deep mud. The nopal's efforts became fran-tic; lights and colors played across Burke's field of vision; the grating sound was an audible croak:

"Gher—gher— gher..."

Burke stopped to rest. The colors crawling before his eyes took on queer forms. If only he could see; if only he would look. . . .

Tarbert, watching him, frowned. "What's the trouble?"

"The nopal is trying to show me something—or letting me see. . . . I'm not looking correctly."

He closed his eyes, hoping to discipline the black smears, the golden whorls, the skeins of fibrous blue and green.

Tarbert's voice came plangent through the darkness. He seemed irritated. "Come, Paul—let's get it over with."

"Wait," said Burke. "I'm getting the hang of it. The trick is to look through your mental eyes—your mind's-eye. The eyes of your analogue. Then you see . . ." His voice dwindled into a soft sigh, as the flickerings steadied and for a brief moment composed themselves. He was looking across a wild strange panorama, composed of superimposed black and gold landscapes, and like a scene through a stereoscopic viewer it was both clear and distorted, familiar and fantas-tic. He saw stars and space, black mountains, green and blue flames, comets, watery sea-bottoms, molecules moving, net-works of nerves. If he chose to use his analogue hand, he could reach to every point of this multi-phase region, and still it extended across a greater and more complicated space than all the familiar universe.

He saw the nopal, much more substantial than the wisps of film and froth he had glimpsed before. But here in this analogue cosmos they were unimportant, secondary to a colossal shape crouching in an indefinable mid-region, a black corpulence in which floated half-unseen a golden nucleus, like the moon behind clouds. From the dark shape issued a billion flagellae, white as new corn-silk, streaming and wav-ing, reaching into every corner of this complicated space. At the end of certain strands Burke sensed dangling shapes, like puppets on a string, like plump rotten fruit, like hanged men on a rope. The fibrils reached near and far. One came into Electrodyne Engineering, where it clamped to Tarbert's head with a sensitive palp like a rubber suction-cup.

Along the strand, nopal clustered; they seemed to be gnawing, rasping. Burke understood that when they gnawed suffi-ciently the fibril would draw back in frustration, leaving a naked unprotected scalp. Directly over his own head waver-ed another of the fibrils, ending in an empty sucker-palp. Burke could follow back along the length of the fibril, across distances which were at once as far as the end of the universe, and as close as the wall; he could look into the focus of the gher. The glazed yellow nucleus studied him with so avid, so intent and intelligent a malice that Burke mumbled and muttered.

"What's the trouble, Paul?" came Margaret's anxious voice. He could see her, too: clearly and recognizably Margar-et, although her image wavered as if caught in a column of heated air. Now he could see many people; if he wanted, he could talk to any of them. They were as far as China but as close as the tip of his nose. "Are you all right?" spoke the vision of Margaret, in wordless words, in soundless sounds.

Burke opened his eyes. "Yes," he said. "I'm all right."

The vision had lasted a second, two seconds. Burke look-ed at Tarbert; they stared eye to eye.

The gher controlled Tarbert; it controlled the Xaxans; it had controlled Burke himself until the nopal had gnawed away the fibril. The nopal—fussy, limited little parasites!—striving to survive they had betrayed their great enemy!

"Let's get started," said Tarbert.

Burke said cautiously, "I want to think things over a bit."

Tarbert studied him with a bland, blind look. Cold eddies played along Burke's nerves. The gher was instructing its agent. "Did you hear me?" asked Burke.

"Yes," said Tarbert in a syrup-sweet voice. "I heard you." His eyes—to Burke's imagination—shone with a dull golden shine.

XI

burke rose to his feet and walked, a slow step at a time. Two feet from Tarbert he halted, looking into the face of his friend, trying to achieve objectivity. He failed; he felt horror and hate.

How much derived from the nopal? Com-pensate! He told himself. Over-compensate!

"Ralph," he said in as even a voice as he could manage, "we've got to make quite an effort. I know what the gher is. It rides you just like the nopal rides me."

Tarbert shook his head, grinning like a haggard gray fox. "That's your nopal talking."

"And the gher talks through you."

"I don't believe that." Tarbert himself was striving for ob-jectivity. "Paul—you know what the nopal are. Don't un-derestimate their cunning!"

Burke laughed sadly. "This is like an argument between a Christian and a Moslem: each thinks the other a mis-guided heathen. Neither of us can convince the other. So— what are we going to do?"

"I think it's important that you be denopalized."

"For the benefit of the gher? No."

"Then what do you suggest?"

"I don't know. This business becomes ever more com-plicated. For the moment we can't trust ourselves to think straight—let alone trust each other. We've got to straighten things out."

"I agree completely." Tarbert seemed to relax, to ponder. Almost absentmindedly he toyed with the floating wad of nopal-stuff, kneading it with vast authority, forming it into a pillow of apparent density.

Careful!

"Let's see if we can find our lowest common denomina-tor of agreement," said Tarbert. "I feel that the denopaliza-tion of Earth is our prime concern."

Burke shook his head somberly. "Our basic duty is—"

"This." Tarbert acted. The nopal-stuff lurched, spun through the air, thrust down over Burke's head. The spines of the nopal momentarily supported, distended the substance; then they crumpled. The pressure on Burke's head was palpa-ble; he felt as if he were smothering. With his fingers he tried to claw the stuff away; with his mind he tried to banish it, but Tarbert had the advantage of impetus. The nopal sud-denly shivered, collapsed like an egg-shell. Burke felt jolt-ing shock, as if a hammer had tapped his exposed brain. His vision swarmed with blazing blue lightning-flashes, bursts of glowing yellow.

The pressure ceased; the lights faded. In spite of his rage at Tarbert's treachery, in spite of the pain and dazzle, he recognized a new state of well-being. It was as if a sod-den head-cold had been cured; as if, while choking, his lungs had opened to fresh air.

He could afford no time for introspection. The nopal was crushed. All to the good; what of the gher? He focused his mental gaze. To all sides floated the nopal, fluttering their plumes like outraged harridans. The arm of the gher hung overhead. Why did it hesitate? Why was its motion so uncertain? It hovered closer, drifted gingerly down; Burke ducked, reached for the tatters of the crushed nopal, at the collapsed mantle of nopal-stuff, pulling it over his head. The sucker slid down again, feeling, exploring. Burke dodged away once more, smoothing the protective mantle about his skull. Margaret and Tarbert watched in wonder. The nopal nearby jerked and quivered in excitement. Far away loom-ed the gher—half the distance of the universe?—bulking like a mountain into the night sky.

Burke became furious. He was free; why should he sub-mit to the gher? He seized a fragment of nopal-stuff in his hand, in the hand of his analogue, whirled it up, beat at the sucker, at the fibril.

The sucker curled back like the lip of a snarling dog, swayed, withdrew in annoyance.

Burke laughed wildly. "Don't like that, eh? I've just started!"

"Paul," cried Margaret. "Paul!"

"Just a minute," said Burke. He slashed at the sucker— again, again. There was restraining friction. Burke looked around. At his side stood Ralph Tarbert, clutching at the nopal-matter, straining against Burke's efforts. Burke pulled and heaved, to no avail. . . . Was this Tarbert, after all? It looked like him, yet with a curious distortion. . . . Burke blinked. He was wrong. Tarbert sat half-sprawled in his chair, eyes half-closed. . . . Two Tarberts? No! One of them naturally would be his analogue, acting at the bidding of Tarbert's mind. But how did the analogue detach itself?

Was it an entity in itself? Or was the separation only ap-parent, the result of para-cosmos distortion? Burke peered into the haggard face. "Ralph, do you hear me?"

Tarbert moved, straightened up in his chair. "Yes, I hear you."

"Do you believe what I told you about the gher?"

There was a moment's hesitation. Then Tarbert gave a great sad sigh. "Yes. I believe you.

There was something— I don't know what—controlling me."

Burke studied him a moment. "I can fight the gher, if you won't resist me."

Tarbert gave a weak laugh. "Then what? The nopal a-gain? Which is worse?"

"The gher."

Tarbert closed his eyes. "I can't guarantee anything. I'll try."

Burke looked back into the para-cosmos. Far away—or was it close at hand?—the orb of the gher flickered with caution and alarm. Burke took a fragment of nopal-stuff, tried to form it, but in the hands of his analogue the stuff was tough and refractory. By dint of great effort Burke worked the material, and finally achieved a lumpy bar. He confronted the far brooding form, feeling trivial, an infinites-imal David before a colossal Goliath. To attack, he must wield the bar across an immense gap. . . . Burke blinked. Was the distance so far? Was the gher, after all, so enormous?

The perspectives twinkled and shifted, like the angles in a visual puzzle—and abruptly the gher seemed to hang no more than a hundred feet away—or perhaps as close as ten feet. . . . Burke jerked back startled. He hefted the bar, swung it sidewise. It struck the black hulk and col-lapsed as if it were foam. The gher—a hundred miles, a thousand miles distant—ignored Burke, the indifference more insulting than hostility.

Burke glowered toward the monstrous thing. The internal orb swam and bulged, the myriad capillaries glistened with silken luster. He shifted his gaze, traced the fibril running to Tarbert's head. He reached out, seized it, pulled hard. There was resistance, then the fibril parted, the sucker fell loose, twitching and squirming. The creature was not ab-solutely invulnerable; it could be hurt! Nopal settled swiftly for Tarbert's unprotected scalp; Burke could see the mental emanations blooming like a luminous flower. One enormous nopal reached the prize first—but Burke interposed a frag-ment of nopal-stuff, encasing Tarbert's head. The nopal drew back frustrated, the orbs solemn and minatory. The gher abandoned its placidity; the golden orb rolled and wallowed furiously.

Burke turned his attention to Margaret. Her nopal glared back at him, aware of its danger.

Tarbert raised his hand to deter Burke from hasty action. "Better wait—we might need someone to front for us. She's still a Chitumih. . . ."

Margaret sighed; her nopal calmed itself. Burke looked back to the gher, now remote, at the end of the universe, swimming in a cool black flux.

Burke poured himself a cup of coffee, settled into a chair with a sigh of fatigue. He watched Tarbert who was star-ing into mid-air with a rapt expression. "Do you see it?"

"Yes. So that's the gher."

Margaret shuddered. "What is it?"

Burke described the gher and the bizarre environment in which it lived. "The nopal are its enemies. The nopal are semi-intelligent; the gher displays what I would call an evil wisdom. As far as we're concerned one is no better than the other. The nopal is more active. It seems that after gnawing about a month it can break the gher's fibril, and displace the gher's sucker-pad. I tried chopping at the gher, unsuccessfully. It's the toughest object there— presumably because of the energy available to it."

Margaret, sipping coffee, looked critically at Burke over her cup. "I though you couldn't be denopalized except by that machine. . . . But now—"

"Now that I lack my nopal, you hate me again."

"Not so much," said Margaret. "I can control it. But how—"

"The Xaxans were quite explicit. They told me that the nopal could not be pulled loose from the brain. They never tried smashing the nopal into a mat. The gher wouldn't allow it. Tarbert was too quick for the gher."

"An accident, pure and simple," said Tarbert modestly.

"Why aren't the Xaxans aware of the gher?" Margaret demanded. "Why didn't the nopal let them see it, or show it to them, as they did with you?"

Burke shook his head. "I don't know. Possibly because the Xaxans aren't susceptible to visual stimuli. They don't see in the sense that we do. They form three-dimensional models inside their brains, which they interpret by means of tactile nerve-endings. The nopal, remember, are flimsy creatures—stuff of the para-cosmos, balloons compared to the bricks we're made of. They can excite relatively feeble neural currents in our minds—enough for visual stimulation, but perhaps they can't manipulate the more massive mental processes of the Xaxans. The gher made a mistake when it sent the Xaxans to organize Earth. It ignored our suscep-tibility to hallucination and visions. So we're in luck—tem-porarily. For the first round at least, neither nopal nor gher have won. They've only alerted us."

"The second round is coming up," said Tarbert. "Three people won't be hard to kill."

Burke rose uneasily to his feet. "If only there were more of us." He scowled toward the denopalizing machine. "At least we can ignore that brutal thing."

Margaret looked anxiously toward the door. "We should leave here—go someplace where the Xaxans can't find us."

"I'd like to hide," said Burke. "But where? We can't dodge the gher."

Tarbert looked off into space. "It's an ugly thing," he said presently.

"What can it do?" quavered Margaret.

"It can't hurt us from the para-cosmos," said Burke. "It's tough, but it's still no harder than thought."

"There's an awful lot of it," said Tarbert. "A cubic mile? A cubic light-year?"

"Maybe just a cubic foot," said Burke. "Maybe a cubic inch. Physical measurements don't mean anything; it's how much energy it's able to turn against us. If for example—"

Margaret jerked around, held up her hand. "Shhh."

Burke and Tarbert looked at her in surprise. They listened, but heard nothing.

"What did you hear?" Burke asked.

"Nothing. I just feel cold all over. ... I think the Xaxans are coming back."

Neither Burke nor Tarbert thought to question the ac-curacy of her feelings. "Let's go out the back way," said Burke. "They won't be here for any good purpose."

"In fact," said Tarbert, "they're here to kill us."

They crossed the workshop to the sliding doors which opened into the dark warehouse, stepped through. Burke slid the doors together, leaving a half-inch crack.

Tarbert muttered, "I'll check outside. They might be watching the back." He disappeared into the dark. Burke and Margaret heard his footsteps echoing stealthily across the concrete floor.

Burke put his eye to the crack. Across the shop, the door into the office eased open. Burke saw a flicker of movement, then the room exploded with soundless purple glare.

Burke staggered away from the crack. A purple flickering light, thick as smoke, followed him.

Margaret grasped his arm, supported him. "Paul! Are you—?"

Burke rubbed his forehead. "I can't see," he said in a muffled voice. "Otherwise I'm all right." He tried to look with the vision of his analogue—which might or might not be similarly affected.

Straining into the dark, the scene began to come clear to him: the building, the screen of cypress trees, the ominous shapes of four Xaxans. Two stood in the office; one patrolled the front of the building; one circled around toward the warehouse entrance. From each, a pale fiber led to the gher. Tarbert was at the outer door. If he opened it, he would meet the approaching Xaxan.

"Ralph!" hissed Burke.

"I see him," Tarbert's voice came back. "I've thrown the bolt on the door."

With hammering pulses they heard the quiet sound of the outside latch being tried.

"Perhaps they'll go away," whispered Margaret.

"Small chance of that," said Burke.

"But they'll—"

"They'll kill us, if we let them."

Margaret was breathlessly silent a moment. Then she asked, "How can we stop them?"

"We can break their connection to the gher. Try to, at least. That might dissuade them."

The door creaked.

"They know we're here," said Burke. He stared into nothingness, willing himself to see through his analogue's eyes.

Two Xaxans had entered the workshop. One of these, Pttdu Apiptix, took a slow stride toward the sliding doors— another and another. Staring into the para-cosmos, Burke traced the fibril which led to the gher. He reached forth his analogue hand, seized it, pulled. This time the struggle was intense. The gher by some means stiffened the fiber, and caused it to vibrate, and Burke felt a pang of vague pain as he heaved and pulled. Apiptix chattered with rage, clutched at his head.

The fibril broke, the palp slipped away. Down upon the crested head plumped a nopal, plumes fluttering complacently, and Apiptix groaned in dismay.

The back door to the warehouse jarred. Burke turned, to see Tarbert twisting at another fibril. It broke, a second Xaxan lost his link to the gher.

Burke looked back through the crack into the workshop. Apiptix stood rigid, as if stunned. Two of his fellows enter-ed the room, to stare at him. Burke reached forth with his analogue hands, broke one of the fibrils. Tarbert broke the other. The Xaxans came to a rigid halt, as if stunned.

No-pal immediately settled on their heads.

Burke, standing with eye to crack, watched in a turmoil of indecision. If the Xaxans had been acting under compul-sion of the gher, all might be well. On the other hand, they were now Chitumih and he Tauptu—an equal incentive to murder.

Margaret tugged at Burke's arm. "Let me go out there."

"No," whispered Burke. "We can't trust them."

"The nopal are back on them again, aren't they?"

"Yes."

"I can feel the difference. They won't bother me." With-out waiting for Burke's reply she pushed open the door, entered the shop.

The Xaxans stood motionless. Margaret approached, con-fronted them. "Why did you try to kill us?"

The chest-plates of Pttdu Apiptix clicked, stuttered; the voice-box spoke. "You did not obey our orders."

Margaret shook her head. "That's not true! You told us we could have a week to make our arrangements. It's been only a few hours!"

Pttdu Apiptix seemed discomfited, uncertain. He turned toward the office door. "We will go."

"Do you still intend to harm us?" asked Margaret.

Pttdu Apiptix made no direct reply. "I have become Chit-umih. All of us are Chitumih. We must be purged."

Burke left the shelter of the warehouse and rather sheep-ishly came forward. The nopal newly established on Pttdu Apiptix ruffled its plumes furiously. Apiptix jerkily raised his hand; Burke moved more quickly. He seized the wad of nopal-stuff, thrust it down upon the Xaxan. The nopal was smashed, felted down over the crested gray head. Pttdu Apiptix staggered to the jolt of pain, peered drunkenly to-ward Burke.

"You are no longer Chitumih," said Burke. "You are no longer a creature of the gher."

"The 'gher'?" inquired the voice-box, ridiculously toneless. "I do not know of the 'gher'."

"Look into the other world," said Burke. "The" world of thought. You will see the gher."

Pttdu Apiptix gazed at him blankly. Burke amplified his instructions. The Xaxan shuttered his eyes, lizard-gray mem-branes folding across the dull surfaces. "I see strange shapes. They make no solidity. I can feel a pressure. . . ."

There was a moment of silence. Tarbert entered the shop.

The Xaxan's chest-plates suddenly rattled like hail. The voice-box gurgled, stammered, apparently balked by con-cepts not included in its index. It spoke. "I see the gher. I see the nopal.

They live in a land my brain cannot form .... What are these things?"

Burke slumped down into a chair. He poured himself some coffee, emptying the pot. Margaret automatically went to make fresh coffee. Burke drew a deep breath, explained what little he knew of the para-cosmos, including the area of his and Tarbert's theorizing. "The gher is to the Tauptu what the nopal is to the Chitumih. A hundred and twenty years ago, the gher was able to dislodge the nopal from one Xaxan—"

"The first Tauptu."

"The first Tauptu on Ixax. The gher provided the original sample of nopal-stuff—where else could it come from? The Tauptu were to become warriors for the gher, crusading from planet to planet. The gher sent you here to Earth, to expel the nopal, to lay bare the brains of Earth.

Eventually the nopal would be eradicated; the gher would be supreme in the para-cosmos. So the gher hoped."

"So the gher still hopes," said Tarbert. "There's very little to prevent it."

"I must return to Ixax," said Pttdu Apiptix. Even the mechanical delivery of the voice-box could not conceal his desolation of spirit.

Burke chuckled morosely. "You'll be seized and penned up as soon as you show your face."

The Xaxan's chest-plates rang with an incisive angry click-ing. "I wear the six-prong helmet. I am Space Lord."

"That makes no difference to the gher."

"Must we fight another war then? Must there be a new division into Tauptu and Chitumih?"

Burke shrugged. "More likely either the nopal or the gher will kill us before we can start any such war."

"Let us kill them first."

Burke laughed shortly. "I wish I knew how."

Tarbert started to speak, then relapsed into silence. He sat with eyes half-closed, attention fixed on the other world. Burke asked, "Well, Ralph, what do you see?"

"The gher. It seems to be agitated."

Burke channeled his own gaze into the para-cosmos. The gher hung in the analogue of the night sky, among great blurred star-spheres. It shivered and jerked; the central orb rolled like a pumpkin in a dark lake. Burke watched in fascin-ation, and seemed to see in the background a wild remote landscape.

"Everything in the para-cosmos has a counterpart in the basic universe," mused Tarbert in a detached voice. "What object or creature in our universe is the counterpart of the gher?"

Burke jerked his gaze away from the gher, stared at Tarbert. "If we could locate the gher's counterpart—"

"Precisely."

Fatigue forgotten, Burke hitched himself forward in his chair. "If it's true for the gher, it should be equally true for the nopal."

"Precisely," said Tarbert a second time.

Apiptix came forward. "Denopalize my men. I wish to observe your technique."

Even without nopal or gher to distort his judgment, there could never be a camaraderie between Earthman and Xax-an, thought Burke. At their best they showed no more warmth or sympathy than a lizard. Without comment he took up the pillow of nopal-stuff and in quick succession crushed the three nopal, matting the fragments over the crested skulls. Then without warning he did the same for Margaret. She gasped, collapsed into her chair.

Apiptix paid her no heed. "These men are now insulated from further nuisance?"

"So far as I know. Neither nopal nor the gher seem able to penetrate the mat."

Pttdu Apiptix stood silent, evidently peering into the para-cosmos. After a moment his chest plates gave a rattle of annoyance. "The gher does not appear clearly to my visual organ. And you see it well?"

"Yes," said Burke. "When I concentrate on seeing it."

"And you can define its direction."

Burke pointed, up and off at a slant. Pttdu Apiptix turned to Tarbert. "You are agreed as to this?"

Tarbert nodded. "That's where I see it, too."

The horny chest-plates gave another rattle of annoyance. "Your visual system differs from mine. To me it appears"— the voice-box chattered as it came upon an untranslatable idea—"in all directions." He stood silently a moment, then said, "The gher has caused my people great hardship."

Something of an understatement, thought Burke. He went to the window. The eastern sky was dim with approaching dawn.

Apiptix turned to Tarbert. "You made remarks about the gher, which I failed to comprehend.

Will you repeat them?"

"With pleasure," said Tarbert politely, and Burke grinned to himself. "The para-cosmos apparently is subsidiary to the normal universe. The gher would therefore seem to be the analogue of a material creature. The same of course applies to the nopal."

Apiptix stood quiet, as he digested the implications of the statement. His voice-box spoke. "I see the truth of all this. It is a great truth. We must seek out this beast and destroy it. Then we must do the same for the nopal. We will find their home environment and destroy it, and in this manner destroy the nopal."

Burke turned away from the window. "I'm not sure that this is an unalloyed blessing. It might do the Earth people great harm."

"In what way?"

"Consider the consequences if everyone on Earth sudden-ly becomes clairvoyant and telepathic?"

"Chaos," muttered Tarbert. "Divorces by the hundreds."

"No matter," said Apiptix. "This must not be considered. Come."

" 'Come'?" asked Burke in surprise. "Where?"

"To our space-ship." He made a motion. "Hurry. Day-light is almost here."

"We don't want to go aboard your space-ship," argued Tarbert in the voice of one reasoning with a petulant child. "Why should we?"

"Because your brains see into the over-world. You will lead us to the gher."

Burke protested; Tarbert argued; Margaret sat in apathy. Apiptix made a peremptory gesture.

"Be quick. Or you will be killed."

The flat intonations gave the threat a dire and immediate significance. Burke, Tarbert and Margaret hastily walked from the building.

XII

the xaxan space-ship was a long flattened cylinder, with a row of turrets along the top surface.

The interior was harsh and comfortless and smelled of Xaxan materials and of the acrid leathery odor of the Xaxans themselves. Above, cat-walks communicated with the turrets. Forward, were controls, dials, gauges, instruments; to the stern, were en-gines hooded under pods of pinkish metal. The three Earth-people were assigned no specific quarters and none seemed available for any members of the crew. When not occupied with one duty or another, the Xaxans sat stolidly on bench-es, occasionally exchanging a rattle of conversation.

Apiptix spoke only once to the Earth-people: "In which direction lies the gher?"

Tarbert, Burke and Margaret concurred that the gher was to be found in that direction marked by the constella-tion Perseus.

"How far, or is this revealed to you?"

None of the three could hazard so much as a guess.

"In this case we will proceed until there is a sensible change in its direction." The Xaxan marched away.

Tarbert sighed ruefully. "Will we ever see Earth again?"

"I wish I knew," said Burke.

Margaret said, "Not even a toothbrush. Not even a change of underclothes."

"You might borrow something of the sort from one of the Xaxans," Burke suggested. "Apiptix is lending Tarbert his electric razor."

Margaret gave him a sour smile. "Your humor is just a trifle misplaced."

"I'd like to know how all of this works," said Tarbert, looking up and down the compartment.

"The propulsion system is like nothing I've ever heard of." He signaled Apip-tix, who after an impersonal and incurious stare, approached. "Perhaps you'll explain the working of the engines to us," Tarbert suggested.

"I know nothing of this matter," stated the voice-box. "The ship is very old; it was built before the great wars."

"We'd like to learn how the engines operate," said Burke. "As you know, we don't even recognize velocities higher than light-speed."

"You may look as you like," said Apiptix, "because there is nothing to see. As to sharing our technology with you, I think it unlikely. You are a volatile and tendentious race; it is not to our interest that you over-run the galaxy." He stalked away.

"A graceless set of barbarians," growled Tarbert.

"They don't display much charm, for a fact," said Burke. "On the other hand they don't seem afflicted with any of the human vices."

"A noble race," said Tarbert. "Would you want your sister to marry one?"

Conversation lapsed. Burke tried to look into the para-cos-mos. He realized a dim image of the ship, which might have been a function of the image-forming faculty of his mind rather than

"clairvoyance," but no more. Beyond was dark-ness.

From sheer fatigue the three slept. When they awoke, they were fed, but otherwise ignored.

They wandered the ship without hindrance, and found mechanisms of incomprehensible purpose, fabricated by methods and procedures which seemed quaint and strange.

The voyage continued, and only the motion of hour—and minute—hands gave a measure of time. Twice the Xaxans performed some operation which allowed the ship to coast in normal interstellar space, in order that the Earth-people could indicate the direction of the gher, after which the course was adjusted and the ship urged once again into motion. During these halts it seemed as if the gher had relaxed from its previous baleful concentration. The yellow orb floated at the top, like an egg yolk in a cup of ink. As to its distance, this was yet indefinite; in the para-cosmos "distance" had no precise measurement, and Burke and Tar-bert uneasily contemplated the possibility that the gher might inhabit a remote galaxy. But on the third half, the gher no longer hung before them, but to the stern, in the precise direction of a dim red star. The gher now was enormous and brooding, and even as they gazed at the black hulk the yellow orb came tumbling around to occupy the frontal surface. It was difficult to evade a sensation that this was an organ of perception.

The Xaxans turned the ship, proceeded back along the way they had come. When they next brought it out of quasi-space, the red star hung below, attended by a single cool planet. Focusing his perceptions, Burke saw the loom of the gher superimposed upon the disk of the planet.

Here was the home of the gher. The landscape of the planet dominated the background: a dark strange land of faintly iridescent swamps and regions of what seemed cracked and caked mud.

The gher occupied the center of the land-scape, its filaments spreading in all directions, the orb roll-ing and pulsing.

The ship went into orbit around the planet. The surface, by telescopic magnification, appeared flat, almost feature-less, marked by an occasional oily swamp. The atmosphere was rare, cold and mephitic. At the poles were tumbles of a black crusty substance, like charred paper. There was nothing to indicate the presence of life, neither artifacts, ruins, or illumination; and indeed the single noteworthy fea-ture of the planet was a great chasm in the high latitudes, a crevasse like a split in an old croquet ball.

Burke, Tarbert, Pttdu Apiptix and three other Xaxans arrayed themselves in air-suits, entered the tender. It de-tached itself from the ship and drifted down toward the surface. Burke and Tarbert, examining the flat panorama, finally agreed on the location of the gher: a small lake or pond at the center of a wide basin, into which the sunlight struck at a long slant.

The tender keened through the upper atmosphere, settled upon a low knoll a half-mile from the pond.

The group alighted into the wan red sunlight, to stand upon a surface of shale and gravel. A few yards distant was a black knee-high growth of what seemed lichen: a crumbling efflorescence, like carbonized cabbage leaves. The sky was purple above, shading to a sulphurous brown at the horizons; the basin was a dismal expanse tinted maroon by the sunlight. At the center, the ground became moist and black, altered first to a glistening slime, then finally to liquid. Humping from the surface was a leathery black sac.

Tarbert pointed. "There is the gher."

"Insignificant, isn't it," said Burke, "compared to its ana-logue."

Apiptix blinked and stared into the para-cosmos. "It knows we are here."

"Yes," said Burke. "It definitely does. It's quite agitated."

Apiptix brought forth his weapon, strode off down the slope. Burke and Tarbert followed, then halted in wonder. In the para-cosmos the gher heaved and convulsed, then began to exude a vapor, which ordered itself into a tall shadow: a semi-human shadow towering—how far? A mile?

A million miles? The gher seemed to loosen, to relax while the shadow condensed, absorbing substance from the gher. It became hard and dense. Burke and Tarbert called out in trepidation.

Apiptix swung around. "What is the mat-ter?"

Burke pointed into the sky. "The gher is building some-thing. A weapon."

"In the para-cosmos? How can it hurt us?"

"I don't know. If it concentrates enough weak energy— billions of ergs—"

"That's what it's doing!" cried Tarbert. "There it is!"

A hundred feet ahead appeared a dense black bipedal body, something like a headless gorilla, eight or ten feet tall. It had long arms ending in pincers; the feet were e-quipped with talons. It hopped forward with sinister intent.

Apiptix and the Xaxans aimed their weapons. A purple blaze struck at the gher-creature, which gave no sign of hurt. Giving a great bound it leapt at the foremost Xaxan. Whether through discipline, fanatic courage or hysteria the Xaxan met its charge, grappled it hand to hand. The fight was short and horrid; the Xaxan was torn apart and his viscera scattered across the caked gray mud. His weapon fell at Tarbert's feet. Tarbert seized it and yelled in Burke's ear: "The gher!"

and set off at a shambling run toward the pond. Burke's knees were like jelly. With great effort he forced himself to follow.

The monster stood rocking on its black legs, torso glow-ing in the blaze of the Xaxan weapons.

Then it turned and lumbered after Tarbert and Burke, who ran across the ooz-ing surface in an episode as terrifying and unreal as the most fearful of nightmares.

Smoking and torn, the creature caught up with Burke, struck him a blow that knocked him cart-wheeling, and con-tinued after Tarbert, who slogged with great effort across the glistening slime. Denser and heavier, the monster floun-dered but lurched forward. Burke picked himself up, look-ed wildly around. Tarbert, now in range of the gher, aimed the unfamiliar weapon. The black creature stalked forward; Tarbert turned a fearful glance over his shoulder, and still fumbling with the weapon tried to dodge aside. His feet slid in the muck; he fell. The monster leapt for-ward, tramped upon Tarbert, then reached down with its pincers. Burke, staggering forward, grappled the creature from the rear. It felt as hard as stone, and as heavy, but Burke was able to thrust it off-balance, and it too toppled into the slime. Burke groped for the weapon, found it, fran-tically tried to find the trigger. The monster pulled itself erect and plunged at Burke, pincers wide. Close past Burke's ear spit a stream of magenta fire. It struck the gher, which exploded. The headless black creature seemed to go porous, then fell apart into shreds and wisps. The para-cosmos frac-tured in a great gush of soundless energy, green and blue and white. When Burke once more regained his extra-world vision the gher was gone.

He went to Tarbert, helped him to his feet; all limped back to solid footing. The pond behind them lay flat and featureless.

"A most peculiar creature," said Tarbert, in a voice still strained and choked. "Not at all nice."

They stood looking at the pond. A breath of the cold air pushed sluggish ripples over the surface. The pool seemed barren and empty, devoid of the meaning which the presence of the gher had given it.

"It must have been a million years old," said Burke.

"A million? Maybe much older." And both Burke and Tarbert looked up at the dim red sun, appraising its past and wondering about the history of the planet. The Xaxans stood in a group not far distant, looking over the pond of the gher.

Burke spoke again. "I'd guess that when it couldn't de-rive sustenance from the physical world it turned to the para-cosmos and became a parasite."

"It's a strange kind of evolution," said Tarbert. "The no-pal must have evolved along similar lines, probably, under similar physical conditions."

"The nopal . . . they seem such trivial creatures." And Burke turned his gaze into the para-cosmos, wondering if nopal were evident. He saw, as before, the ranked land-scapes, the intricate foliations, the mapped connections, the pulsing lights. Certain far nopal—riding Xaxans?

or Earth-folk? he couldn't be sure—surveyed him with malevolent distrust. Elsewhere were others, with bulging eyes and vi-brating plumes. These, so it seemed, were small and un-developed, and seemed to flow in a stately parade from somewhere near at hand. This judgment might well be faul-ty, so deceptive were all appraisals of distance. As he stud-ied the nopal, wondering as to their nature and where they derived he heard Tarbert's voice. "Do you get the impression of a grotto?"

Burke peered into the para-cosmos. "I see cliffs—irreg-ular walls. A crevasse? Would it be the same one we saw coming down?"

Apiptix called to them. "Come. We return to the ship."

His mood seemed morose. "The gher has been destroyed. There are no more Tauptu. Only Chitumih. The Chitumih have won. We will alter this."

Burke spoke hurriedly to Tarbert. "It's now or never. We've got to make a move."

"How do you mean?"

Burke nodded toward the Xaxans. "They're ready to wipe out the nopal. We've got to hold them off."

Tarbert hesitated. "Do we have any option?"

"Certainly. The Xaxans couldn't find the gher without our help. They won't be able to find the nopal. It's up to us."

"If we can get away with it. ... There's a possibility that with the gher gone they might relax, see reason."

"We can try. If reason doesn't work, we've got to use something else."

"Such as what?"

"I wish I knew."

They followed the Xaxans up the slope toward the ten-der. Burke stopped short. "I've had a thought." He ex-plained his idea to Tarbert.

Tarbert was dubious. "What if the stage effects don't come off?"

"They've got to come off. I'll do the reasoning; you take Care of the persuasion."

Tarbert gave a mournful laugh. "I don't know if I can persuade that hard."

Pttu Apiptix, standing beside the tender, motioned to them brusquely. "Come. There is still our final great task: we must destroy the nopal."

"It isn't quite that simple," said Burke cautiously.

The Xaxan held his gray arms wide, fists clenched, each knuckle a knob of white bone: a gesture of exultation or triumph. The voice from the box was nevertheless flat and unaccented.

"Like the gher, they must have their kernels in the base universe. You located the gher without difficulty, you shall do the same for the nopal."

Burke shook his head. "Nothing good would come of it. We've got to think of something else."

Apiptix abruptly dropped his arms, peered at Burke with topaz eyes. "I fail to understand. We must win our war."

"Two worlds are involved. We must consider the best in-terests of both. For Earth any sudden destruction of the nopal would mean disaster. Our society is based upon in-dividuality, privacy of thought and intent. If everyone sud-denly achieved a psionic capacity, our civilization would become chaos. Naturally we do not care to inflict this dis-aster upon our planet."

"Your wishes are immaterial! We are the ones who have suffered and you must follow our instructions."

"Not when they're irrational and irresponsible."

The Xaxan considered him a moment. "You are bold. You must know that I can force you to obey me."

Burke shrugged. "Conceivably."

"You would tolerate these parasites?"

"Not permanently. In the course of years we shall either destroy them or make them socially useful. Before this happens we'll have had time to adjust ourselves to psionic realities. And another consideration: we have our own war on Earth—the 'cold war,' against a particularly odious kind of enslavement. With psionic capabilities, we can easily win this war, with a minimum of bloodshed, to the ultimate benefit of everyone. For us, we gain nothing and lose every-thing by destroying the nopal—at this moment."

The flat tones of the Xaxan's voice-box were almost sar-donic. "As you remarked, the interests of two worlds are involved."

"Precisely. To destroy the nopal would injure your world as much as ours."

Apiptix jerked back his head in surprise. "Absurd! After a hundred and twenty years you expect us to stop short of our goal?"

"You are obsessed with the nopal," said Burke. "You forget the gher, which forced the war upon you."

Apiptix looked off toward the sullen pond. "The gher is dead. The nopal remain."

"Which is fortunate, since they may be crushed and used as protection—against themselves and all the other para-sites of the para-cosmos."

"The gher is dead. We shall destroy the nopal. Then we will need no more protection."

Burke gave a short laugh. "Now who's absurd?" He pointed to the sky. "There are millions of worlds like this one. Do you think the gher and the nopal are unique, the only creatures who inhabit the para-cosmos?"

Apiptix drew back his head like a startled turtle. "There are others?"

"Look for yourself."

Apiptix stood rigid, straining to perceive the para-cosmos. "I see shapes I cannot understand.

One in particular—an evil creature . . ." He looked at Tarbert who stood staring fixedly into the sky, then returned to Burke. "Do you see this creature?"

Burke looked into the sky. "I see something almost like the gher. ... It has a bulging body, two large eyes, a beaked nose, long tentacles. . . ."

"Yes. This is what I see." Apiptix stood silently. "You are right. We need the nopal for protection.

Temporarily at least. Come; we will return."

He marched away up the slope. Burke and Tarbert came behind. "You project a vivid octopus,"

said Burke. "It even gave me a twinge."

"I almost tried a Chinese dragon," said Tarbert. "The octopus was probably more legitimate."

Burke halted, searched the para-cosmos. "We really weren't conning him. Not altogether.

There must be other things like nopal and gher. I seem to see something far far away— like a tangle of angle-worms. . . ."

"Sufficient into the day the evil thereof," said Tarbert in sudden exhilaration. "Let's go home and scare hell out of the commies."

"A noble thought," said Burke. "We've also got a hundred kilograms of gold in the back of my car."

"Who needs gold? All we need is clairvoyance and the black-jack tables at Las Vegas. It's a system nobody can beat."

The tender swung up from the ancient planet, slanting a-cross the great crevasse which split the surface to an un-known depth. Looking down Burke saw puffs and plumed shapes drifting up, moving across space to a place in the para-cosmos where a distorted but familiar globe shone a lambent greenish-yellow.

"Dear old Nopalgarth," said Burke. "Here we come."