Why was Inspector Lognon, married to a sick wife to whom he was devoted, sometimes sharing a fourth-floor apartment on Avenue Junot with a beautiful woman called Marinette Augier? And why was he shot as he left the apartment one night? Now lying in critical danger in hospital, he is unable to offer any explanation. But Maigret knows him as a conscientious, hard-working policeman, even though he had a 'talent for attracting misfortune'.

Maigret soon discovers that Lognon was not having an affair but was, in fact, staking out an apartment on the opposite side of the avenue from Marinette's apartment. He was doing it on his own initiative, so no one knew about it. Which apartment was he staking out? And why? Maybe Marinette Augier can help? But there is a complication: She's disappeared. Maigret calls on Norris Jonker, a rich, arrogant art collector who lives in a grand apartment across from Marinette's apartment with his beautiful wife Mirella, who was formerly married to a ball-bearing manufacturer from Manchester. Is he involved? Is his wife? Maigret discovers a strange room in Jonker's house with a bed and the walls covered in graffiti. This leads him into the dark world of artistic arrogance, art forgery and money.