Michel Piccoli plays a police inspector whose best friend is murdered on the orders of gang boss Charles Vanel. The inspector knows full well that Vanel is too crafty and well-connected to ever stand trial for his crime, so he carefully lays a subtle trap for his adversary. Unfortunately, both Piccoli and Vanel are thwarted by a pair of scheming females.

Fred, the nephew of a senator,has murdered a Black man on a train. The two only witnesses are Lizzie McKay, a prostitute from New York, and Sidney, a colored man. Fred decides to seduce Lizzie in order to make her give false evidence according to which Sidney has attempted to rape her. The uncle also puts pressure on the young woman. After much hesitation, Lizzie finally accepts but Sidney, who has nearly got lynched, takes refuge at her home...