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.

Vincent Bruce, a war veteran, begins working as an occupational therapist at Poplar Lodge, a private psychiatric facility for wealthy people where he meets Lilith Arthur, a charming young woman suffering from schizophrenia, whose fragile beauty captivates all who meet her.