When an employee at an illegal gambling den dies suspiciously, her sister, Nancy, looks into the situation and falls for Johnny O'Clock, a suave partner in the underground casino. Selfish and non-committal by nature, Johnny slowly begins to return Nancy's affection and decides to run away with her, but conflict within his business threatens their plans. As Johnny tries to distance himself from the casino, his shady past comes back to haunt him.
Movie star Charlie Castle draws the ire of Hollywood producer Stanley Hoff when he refuses to sign a new seven-year contract. Castle is sick of the low quality of the studio's films and wants to start a new life. While his estranged wife supports him in the decision, Castle's talent agent urges him to reconsider. When Castle continues to be uncooperative, Hoff resorts to blackmail in order to get his way.