In a Montparnasse cafe, Willy Ferrièrre (Gaston Jacquet), a gambler living beyond his means, suggests out loud that he would pay 10,000 francs for someone to kill his wealthy aunt so he can claim his inheritance.

A shadowy figure emerges (later revealed to be Radek (Vàlery Inkijinof), a Czech emigré) who assures Heurtin that he will clean up the prints and tells him to hide out.

The murder case is assigned to Inspector Maigret (Harry Baur), whose men follow the clues left to discover Heurtin's identity and track him to his parents' house in Versailles, where he has been hiding.

Suspecting that a third person is involved in the murder, Maigret has several encounters with Radek, who all but confesses to the "perfect crime," but Heurtin is able to escape from police surveillance.

Though officially removed from the case for letting Heurtin escape, Maigret suspects that Radek will lead him to the person who first hired the murderer.