Cashier Maurice Legrand is married to Adele, a terror. By chance, he meets Lucienne, "Lulu", and make her his mistress. He thinks he finally met love, but Lulu is nothing but a streetwalker, in love with Dede, her pimp. She only accepts Legrand to satisfy Dede's needs of money.
A lieutenant of the French navy, ready to kill himself in despair, renounces his project after spending a night with a beautiful stranger, the Princess of Lystrie.
A poor boy lives in the attic of a luxury house. During a party, he pays court to an elegant young woman who, without warning him, surprises him at his home.
Maigret investigates in Concarneau where the passage of a yellow dog accompanies a series of murders, sowing terror in the population. The police seem helpless. It must be said that it has no significant evidence.
The Marquise de Langrune invites her friends at her castle in Beaulieu. Among them is Lord Beltham who also came to bring her a significant sum of money. The mysterious Fantômas kills the Marquise during the night. Inspector Juve is sent on his trail.