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

In my “cellar” where case workers all the people of a great hotel, the head of the café, Donge, finds the corpse of Mrs Petersen, a rich client. The investigation by Maigret allows him to rub the husband of the victim, a Swede, Teddy, Ms Petersen’s son, his housekeeper, a social dancer and Donge himself who is the natural father of Teddy. The child he will go to his real father or not he will leave the rich Petersen who adores? The murder mystery and enigma sentimental are resolved by Maigret.

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.