A young man, Alain Lagrange, visits Maigret's apartment while he is out. He leaves before Maigret returns, taking the revolver Maigret had received as a gift from the FBI. That evening Maigret dines at the Pardons, where François Lagrange, Alain's father and an old schoolmate of Pardon's, had been expected, but didn't appear due to ill health. Pardon mentions Lagrange's son, which leads Maigret to visit Lagrange on the off chance that his son was the one who stole the revolver. Leaving Lagrange's, Maigret chats with the concierge, who mentions that Lagrange had been well enough to go out the night before with a heavy trunk. Maigret investigates and finds Deputy André Delteil's body in the trunk at the Gare du Nord. Lagrange refuses to talk at all, seemingly mad.
A policeman had spotted a man matching Alain's description outside an apartment on Boulevard Richard-Wallace, where Maigret discovers that Jeanne Debul, who had known Lagrange, lived. She had just left for London. Maigret finds that Alain has also taken a plane to London, and so he follows them. He finds Alain hiding under a bed in Debul's hotel room, waiting to shoot her, believing that she had been the cause of his father's hardships. Actually, she was apparently an extortionist, using Lagrange to collect for her. He had apparently decided to try to get more from Delteil for himself, and in the process, wound up shooting him with his own gun. Maigret convinces Alain to give up his plan, takes him under his wing, and they return to Paris, where Maigret expects one day to find a reason to arrest Debul.
This report prepared by Dana Samson