Petrus, a Montmartre photographer, is accidentally wounded by Migo, a dancer at the Frou Frou night club, when she is trying to shoot her faithless lover Rodrigue, a counterfeiter. Though Petrus tries to reconcile the lovers, Migo lands up with him after Rodrigue is finally killed by another jealous dancer.

A young novitiate witnesses a murder. Later, she recognizes the culprit, who admits to the killing; the sister works to convince him to turn himself in to the police.