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!

An old lady believes that there has been an intruder in her apartment, but before Maigret has a chance to investigate, he learns that she has been murdered in her apartment.

Maigret sets out to catch a serial killer.