Someone has taken Maigret's favorite pipe, and he remembers that he'd left his office briefly while Mrs. Leroy and her son Joseph Leroy were there. The boy had done it! But the next morning Mrs. Leroy shows up again, to report, not that someone has been coming into the house in Charenton while she was out, as she had yesterday, but that Joseph has disappeared. Lucas tracks down Joseph's girlfriend, Mathilde, and a check on the people who had been lodgers at Leroy's shows that one, Stéphane Bleustein, a foreigner, had been killed. Maigret, Lucas and Mathilde go to an inn at Chelles, on the Marne, where Mathilde and Joseph had once gone. There Maigret finds a recently released criminal, Nicolas, and captures him when he tries to escape. Upstairs, Joseph had barricaded himself into his room in fear of Nicolas. Bleustein had stolen diamonds, and Nicolas had killed him after learning he'd hidden them at Leroy's. But he'd been imprisoned soon after, and when he got out, three months earlier, started searching the Leroy's house when no one was home. Joseph discovered the diamonds, but Nicolas showed up, and Joseph fled to Chelles, where Maigret saved him, recovered the diamonds, and got his favorite pipe back.
This report prepared by Dana Samson