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.
Dick Powell
as Johnny O'Clock
Evelyn Keyes
as Nancy Hobson
Lee J. Cobb
as Inspector Koch
Ellen Drew
as Nelle Marchettis
Nina Foch
as Harriet Hobson
Thomas Gomez
as Pete Marchettis
John Kellogg
as Charlie
Jim Bannon
as Chuck Blayden
Mabel Paige
as Slatternly Woman Tenant
Phil Brown
as Phil, Hotel Clerk
Fred Aldrich
as Hotel Doorman
George Alesko
as Practical Dealer
