At four in the morning, the striptease dancer Arlette from the nightclub Picratt’s drunkenly arrives at the police station in Montmartre. She overheard a conversation in the club: a countess is to be murdered, but she doesn’t know more than that. At nine o'clock, Arlette retracts her statement at the Quai des Orfèvres. By eleven o'clock, she is found strangled. Shortly thereafter, the morphine-addicted Countess Farnheim is also dead. To find the murderer, Maigret must explore the darker sides of Paris. Maigret's 36th case takes place at Place Pigalle and in Montmartre.