Jo Guardini, now the peaceful owner of a charming inn by the banks of the River Marne, once was a dreaded gangster. The respectful citizen does not want to have anything to do with the underworld any more. Unfortunately, two of his former accomplices kidnap a little girl and decide to hide her in his hotel. What will Jo do : side with the law in the person of inspector Loriot or have a relapse in crime?

Without seeming to touch it, journalist Trupeau is interested in the doings of Mireille, a jewelry store saleswoman. A certain Jojo is hanging around the young girl, and not for the right reasons, but to pull off a "heist". Although one of his men betrays him and has to be shot, Jojo succeeds. The police investigate, question and pursue Mireille. Exasperated and disillusioned, the pretty salesgirl shoots Jojo. Fortunately, the journalist is there to prove that she's as white as an ermine. And the ch timents rain down on the culprits.