Synopsis: Three years after song-and-dance man Dick Powell reshaped his nice-guy image by playing hard-boiled gumshoe Phillip Marlowe in Murder My Sweet, he returned to film noir with this crime-based thriller. Johnny O'Clock (Dick Powell) and his partner Pete Marchettis (Thomas Gomez) operate a gambling casino that has seen better days. Chuck Blayden (Jim Bannon), a cop on the take, wants in on the casino, and he makes friends with Pete while trying to convince him that Johnny, the smarter of the two, should go. When Chuck's girlfriend Harriet (Nina Foch) is found dead, a supposed suicide, his sister Nancy (Evelyn Keyes) smells a rat, especially after Chuck skips town. Nancy is convinced that her sister was murdered, and she asks Johnny to help her prove it. Johnny, who already has a number of women in his life -- including Nelle (Ellen Drew), Pete's wife -- figures that one more can't hurt and agrees to help her. But Police Inspector Koch (Lee J. Cobb), convinced that Johnny and Pete were behind Harriet's death, is making it hard for Johnny to do much investigating, and matters get worse when Chuck's body is found floating in the river. Screenwriter Robert Rossen made his directorial debut with this film, 14 years later, he would return to this film's tough, gritty style for his best picture, The Hustler.