In 1892, in New York's Bowery, singer and femme fatale Lady Lou is mistress to saloon proprietor Gus Jordan, who is running for sheriff, but maintains a counterfeit money racket.  Jordan's rival, Dan Flynn, intends to expose Jordan and win the office of sheriff, as well as Lou.  When pretty runaway Sally tries to commit suicide in Gus's tavern, Lou comes to her aid, and Gus and his accomplices, Serge Stanieff and Russian Rita, give her a job picking pockets on the Barbary Coast.

Later Lou visits her jailed ex-lover, Chick Clark, whom Flynn helped send to prison for stealing diamonds for Lou, and Chick demands that she remain faithful to him.  Lou falls for Captain Cummings, the handsome and pious preacher of the mission next door, however, and arranges for his mortgage to be paid.

A string of incidents then puts Lou in a tight spot: after Flynn tells her a new detective in town called "The Hawk" is going to expose Gus, Cummings demands to know Sally's whereabouts, but Lou swears she knows nothing of Gus's business.  Chick then breaks out of jail and nearly chokes Lou, begging her to run away with him.

Next, Serge answers Lou's long-standing invitation to visit her boudoir and, in Rita's presence, confesses his love for her, while giving her a diamond brooch that belongs to Rita.  In a jealous rage, Rita attacks Lou with a dagger, and Lou accidentally kills her, then orders her henchman, Spider, to dispose of the body.

As Lou performs that night, Chick comes to pick her up and hides in her room, while Lou gives Flynn a signal from the stage to meet her there as well.  Chick shoots Flynn dead just as Cummings, who is really The Hawk, raids the saloon, arresting Serge, Gus, Spider and Chick.  Cummings then escorts Lou, who insists on wearing her wrap, to the police wagon, but lifts her into a coach instead.  There, he removes her diamond rings and replaces them with one of his own, telling her, "I'm gonna be your jailer for a long, long time."