Maigret has followed a seedy-looking man to to a low-class hotel in Bremen after he saw him in Brussels wrapping up a package of 30,000 francs and sending it as printed matter. The man had bought a cheap suitcase, and M, on a whim, had bought a similar one, exchanging his with the man's when he had a chance. Watching through a keyhole M sees the man open the suitcase and find it empty. He immediately pulls out a gun and kills himself. The suitcase had contained only an old suit, torn and bloodstained, too large for the man himself. His passport showed Louis Jeunet, but it was a forgery. At the mortuary a man came to view the body, Joseph Van Damme, who tells M he'd just been curious, but takes him to lunch and talks too much.
Returning to Paris, M stops for a moment to buy some tobacco and one of his suitcases is stolen, but not the one with the clothing. At his office, Louis Jeunet's wife appears — she'd recognized his photo in the papers. A call from Rheims — a café keeper had recognized the photo. M goes to Rheims, where the man, Émile, says he'd seen Jeunet go off with Maurice Belloir, Vice-Chairman of a bank. M goes to Belloir's house, where he is surprised to find Joseph Van Damme once more, and two other men, Gaston Janin and Jef Lombard, all originally from Liège. All deny knowledge of Louis Jeunet. Van Damme offers M a ride back to Paris, and when they stop on the way, he tries to push M into the river. M takes him back to his office where Van Damme refuses to say anything and M lets him go.
Shortly afterwards, Armand Lecocq d'Arneville appears, who has also recognized Jeunet's photo. He says it was his brother, Jean, who'd been born in Liège. He recognized the names Belloir and Van Damme. Lucas had followed Van Damme, who left for Liège. M goes there, and visits the tailor where the blood-stained suit was made, but the tailor had died. He goes to Jef Lombard's photo-engraving shop, where he finds Van Damme again. Lombard's wife has just given birth to a baby girl. On the walls of his office are drawings of hanged men, made ten years earlier. M starts to check the newspaper offices for articles from ten years earlier, but each time Van Damme has gotten there first and taken away the February 15 articles. A note calls M to a meeting at a café — Belloir, Lombard and Van Damme are all there, and no one talks. On leaving, someone shoots at M, but misses. M finally gets to Town Hall before Van Damme, and reads the article. Émile Klein had hanged himself on the door-knocker of the Saint-Pholien church ten years earlier.
M goes to Klein's address, where he finds a garret, and once more, Van Damme is there. Soon Lombard and Belloir arrive and the story comes out. They'd all been members of a club they'd called the Companions of the Apocalypse, drinking, philosophizing, sketching... One night, in a drunken stupor, Klein had killed a man, Willy Mortier, after they'd been talking about whether they could. The others had dumped the body in the river, and it had never been found. Jeunet (Jean Lecocq d'Arneville) had never recovered from the event, and kept the bloody suit Belloir had worn, extorting money from the others over the years, which he burnt. They'd come together when Van Damme had learned of Jeunet's suicide. In a month or so the ten-year limit would be up. M, considering all their children, lets the case drop.