Maigret is secretary of the Saint-Georges Police Station under Superintendent Maxime Le Bret, the most worldly of all Paris superintendents. Late one night a young musician, Justin Minard dashes in. He'd seen a woman cry for help from a window on the Rue Chaptal, and heard a shot. He'd rushed to the door, but been thrown out by Louis Viaud, the butler. Checking his street guide, Maigret discovers it is the most prestigious house in the district, that of the Gendreau-Balthazars, of Balthazar Coffee.
Nevertheless he accompanies Minard there, where he is welcomed facetiously, and assured nothing is wrong. They are social acquaintances of Le Bret. The next day Le Bret is inclined to ignore his report, except that he has spotted a lie — Lise Gendreau-Balthazar, who they'd said was in the country at Anseval, he knows from his wife to have been in Paris. He gives Maigret leave to follow up on the investigation on his own, 'on vacation'. Minard insists on helping, and starts by going to Conflans to find Germaine Baboeuf, the maid Lise Gendreau-Balthazar apparently impersonated the night of the shot. He brings her to Paris, where she informs Maigret of some of the details of the household. Maigret spots the car that had been seen waiting near the house that night, and it leads him to Dédé of a garage on the Rue des Acacias, and the Count, Bob d'Anseval, who was apparently seeing Lise. He meets Dédé, and becomes convinced that it was Bob who was killed that night. But Dédé recognizes him as police, tries to get him drunk, and has his accomplice, Albert, bash him over the head so they can make their escape.
Maigret recovers in time to have the police stop them at the Gare de Nord, where Maigret has figured them to be going to Belgium. The next day Le Bret tells him he's done a fine job, and he can finish it up, but he is blocked everywhere he turns, and the newpapers report that the butler had killed a burglar. Someone higher up had decided that discretion was the best policy. Maigret eventually meets Dédé again, who invites him to lunch and tells him, off the record, what has happened. Between them they decide that Lise probably shot Bob accidentally. He was buried in the yard. Had she married him, a d'Anseval, she would have inherited all the money from her grandfather, rather than sharing it with her brother. Bob didn't want to do it, and was there to say so, Dédé waiting outside. Lise's brother paid him to say nothing. The case is closed, and Maigret is promoted to the Quai des Orfèvres, to work under Chief-Inspector Barodet, his hero.
This report prepared by Dana Samson