Picpus is a street and a subway stop where a number of murders have been committed. Maigret tries to find the killer.

Cecile, a young girl who goes to the offices of the Judicial Police several times in a row to complain about nightly visits to the apartment she occupies with her aunt, is not taken seriously by the police until she the day she is found murdered.

Maigret is called to the high-class Hotel Majestic to investigate a body. The wife of a wealthy American has been killed - but to Maigret's surprise she has a gun in her purse. He begins to follow up the handful of clues that could explain her secret life and her demise.