Maigret's patience is tested when the crime boss he has investigated for years, Manuel Palmari, commits another jewellery heist. But when Palmari himself is murdered, Maigret works with the criminal's shady mistress, Aline, to find the killer.

Alfred Jussiaum is a safecracker. While he's on the job he finds the dead body of a woman in the house he's robbing. Afraid, he leaves town and asks his wife Ernestine to go to inspector Maigret and report the murder. Maigret goes to the house and the owner a dentist who lives with his mother denies there ever was a robbery much less a murder. Maigret is not convinced and he soon finds out that the doctor's wife who supposedly travelled to Holland the day of the murder hasn’t reached her destination and is nowhere to be found. Someone is lying!

A schoolmaster from a small fishing village arrives at Maigret's office claiming he's about to be wrongly arrested for murdering the town's disliked postmistress. Maigret travels to the village and discovers a conspiracy of vast proportions amid surly, distrusting villagers.

Maigret responds to a warning that a crime is to be committed in the church in his home town during the first mass on All Soul's Day.

Maigret sets out to catch a serial killer.