When practicing for a role, actor Jack is mistaken for the killer Ace. He doesn't realize this until it's too late and is carried off to gangster boss Leo Smooth, who wants Ace to do a job for him. Fearing for his life, Jack plays his role, but always searching for a way out of the well-guarded house.

On his way home after doing a bit on television, struggling actor Jack Albany, thinking that he is being followed by a mugger, ducks into an open doorway and is confronted by a young hoodlum, Florian, who mistakes him for Ace Williams, a notorious hired killer he has been assigned to meet. Fearing for his life, Jack does not correct the error and is driven to the estate of Florian's employer, gangster Leo Joseph Smooth, who is a lover of art. Smooth is planning to steal a painting recently acquired by a New York museum. Desperate, Jack tries to convince Smooth's pretty art instructress, Sally Inwood, that he is not really Ace Williams, but she refuses to believe him. When the real Ace appears, Smooth locks the two men in a room to determine which of them is the killer. Aided by a now-convinced Sally, Jack emerges as the victor; and the next afternoon he joins Smooth's gang for the raid on the museum. Once there, however, he prevents the mobsters from taking the painting and leads them on a wild chase from one gallery to another, ending up in a pop art exhibition. While Jack is holding his adversaries, the police, alerted by a telephone call from Sally, arrive on the scene and round up the would-be thieves. Acclaimed as a hero, Jack wins both Sally and enough publicity to assure future acting offers.