Ruby Carter, Mae West is the beautiful Vaudeville star and headliner at a nightclub in St. Louis in the early 1890s. She is romantically involved with Tiger Kid, Roger Pryor, a prizefighter. To get the preoccupied Tiger Kid to focus on his training, his trainer arranges for another boxer to stage a supposed infidelity. Heartbroken, the Tiger Kid sends her a breakup letter.
Ruby's agent, Edward Gargan, convinces her to take a high-paying contract for a residency at the Sensation House in New Orleans, where Ace Lamont installs Ruby in a suite adjacent to his own. She quickly makes a name for herself, drawing fans and suitors, and even receives a diamond necklace from one admirer. Lamont is attracted to her but resents her wealthy suitors, as they prevent him from controlling her. Lamont is romantically linked with Molly Brant, Katherine DeMille, whom he continually disregards.
Unbeknownst to Ruby, the Tiger Kid, Roger Pryor, comes to New Orleans and is chosen as a contender in a title fight hosted by Lamont. Lamont tells the Tiger Kid that the cost of the title fight has put him under financial pressure; Lamont lies that he had given a diamond necklace to a woman who was blackmailing him. Lamont pressures the Tiger Kid into acting as a robber to “steal back” the jewels; he plans a carriage ride together with Ruby along a dark stretch of waterfront. The set-up works and a masked Tiger Kid takes Ruby's jewelry and flees, but doesn't recognize her face in the darkness. Ruby pointedly comments that the robber didn't take Lamont's ring. Her suspicions are confirmed later, when she sees Lamont and the Tiger Kid meet in the lobby and slip upstairs. From the adjoining room, she sees the Tiger Kid hand Lamont her jewelry, which Lamont locks in his personal safe.
Ruby continues to perform at the Sensation House in the days leading up to the fight. She sets a trap by giving Lamont other jewelry for safekeeping, then uses opera glasses to note the safe's combination from a distance. She suspects a fix is in, and tells her suitors to bet heavily against the Tiger Kid. In the ring, the Tiger Kid puts up a strong fight, but is finally knocked out after thirty rounds, shortly after Lamont had given him a bottle of water.
After the match, Ruby and the Tiger Kid reconcile, when he realizes she had been faithful to him in St. Louis; in turn, she tells him Lamont had likely drugged him. That evening, Lamont tells Ruby that covering all of the bets will nearly ruin him, and plans instead to set fire to the Sensation House and abscond with the contents of his safe and flee with her to Havana. She, however, has already cleaned out his safe and instructed her maid Jasmine, Libby Taylor, to pack her bags and get a cab waiting. Lamont locks Molly in a closet and pours lamp oil around the room, but before he can set the fire, the Tiger Kid confronts Lamont, killing him with a single punch. Ruby inadvertently lights the room on fire with a discarded cigarette. She and the Tiger Kid rescue Molly and call the fire department. A series of newspaper headlines appears on screen, showing the Tiger Kid is charged with, and cleared, of killing Lamont. The final scene shows Ruby and the Tiger Kid getting married in front of a justice of the peace.
