In St. Louis in 1892, singer Ruby Carter appears in the stage show My American Beauty, then goes home with prizefighter Tiger Kid, who forces her to swear fidelity to him.  Tiger's manager, Kirby, schemes to keep Tiger from Ruby, and when one of the men at the gym calls Ruby pretending to be her lover, a heartbroken Tiger writes Ruby a good-bye letter.  Ace Lamont, who runs the "Sensation House" saloon in New Orleans, then offers Ruby a contract and she accepts.

In New Orleans, Ruby becomes the object of Ace's girlfriend Molly Brant's jealousy, while becoming a big success with the men of New Orleans.  Among them is the wealthy Brooks Claybourne, who gives Ruby diamonds.  Ace, meanwhile, hires Tiger to enter into a fixed fight against Battling Bruce, and Tiger arrives in New Orleans, unaware of Ruby's proximity to him.  When Ace asks Tiger to steal the jewels he gave a woman so he has the money to sponsor Tiger's fight, Tiger unsuspectingly robs Ruby while she rides in a coach with Ace.

Later, Ruby sees Ace hiding her jewels in a wall safe.  Tiger then visits Ruby and swears his love, and the man from the gym confesses to his phone prank.  That night, Ruby joins a Black revival meeting and vows to return the diamonds to Brooks.

On the evening of the fight, Ruby gives her remaining diamonds to Ace for "safe-keeping" and watches him as he opens the safe.  Knowing Ace has bet heavily on Tiger, Ruby puts a sedative in Tiger's water bottle and he loses.  Terribly in debt to his patrons who bet on Tiger, Ace schemes to set fire to the Sensation House and flee to Havana with the diamonds and Ruby, who pretends to love him, then steals the diamonds for herself.  Ace then tricks Molly into believing he still loves her and locks her in a closet before dousing the room with lamp oil.

In Ruby's adjacent room, Tiger threatens Ruby for tipping off Brooks to Bruce's victory, and she swears Ace drugged the water and is clearing out of town.  Tiger punches Ace, who has a gun, and Ace hits his head and dies instantly.  Ruby accuses Tiger of being a thief and a murderer, then discards her cigarette, inadvertently starting a fire.  Molly wakes up in the closet and screams and Tiger rescues her while Ruby calls the fire department.

Tiger goes to trial for Ace's murder, but eventually he is exonerated and he and Ruby marry.