Maigret had been receiving regular visits from Miss Cécile Pardon, who claimed that someone was coming into her house at night and rearranging the furniture. It had become a joke at the Quai des Orfèvres. But this time when she came and left a message that "something terrible happened last night," she has disappeared by the time Maigret gets around to calling for her. Maigret goes to her house in Bourg-la-Reine, and discovers that her aunt, Mrs. Juliette Boynet, the owner of the building, with whom Cécile had lived, has been strangled. Later Cécile's body is found in a closet in the Police Judiciaire, also strangled, and her purse missing.
Maigret discovers that Cécile's out-of-work brother, Gérard Pardon, had slipped into the building the night of the aunt's murder. Juliette's downstairs neighbor, Mr. Charles Dandurand, a disbarred lawyer, had been her business manager, helping her acquire interest in numerous houses. He had been the one moving the furniture, and her aunt had drugged Cécile's herb tea on those nights he came for business meetings. But the night Gérard came, he drank her tea by chance, and so Cécile had heard everything.
Confronting her aunt, she wound up strangling her, but Mr. Charles, in the apartment below, had overheard what happened. Realizing that she had the papers which would show that he and Juliette had killed Juliette's husband, Mr. Charles follows Cécile to the Quai Des Orfevres, where he induces someone to bring her to him. He kills her and leaves her body in a closet, taking the incriminating papers. But Juliette had sent an incriminating letter into safekeeping with a relative in the country, and Charles's guilt is established.
This report prepared by Dana Samson