Seaman Michael O'Hara (Orson Welles) is hired as to work on the yacht of the wealthy Arthur Banister (Everett Sloane). Michael has already met Bannister's beautiful wife Elsa (Rita Hayworth) saving her from a mugging earlier. having set sail, Bannister's law partner, George Grisby (Glenn Anders) offers Michael $5,000 to help him fake his own murder, so that he can collect his insurance. Grisby convinces Michael to sign a confession, telling him that he'll never be convicted since there won't be a body. Since Michael has started an affair with Elsa and wants to run away with her, he agrees. But it's a double-cross: Private Eye Sydney Broome (Ted De Corsia) has discovered that Grisby is planning to kill Bannister, frame Michael from Bannister's murder, and disappear, apparently murdered himself. After Michael has gone through with the sham murder, Broome, mortally wounded by a shot from Grisby, warns Michael. He rushes to Bannister's office to find Bannister still alive and Grisby dead. The signed confession means he's put on trial for Grisby's murder. Bannister is keen to defend Michael. His advice is to make a plea of Justifiable Homicide, since the evidence against him is so great. But can Michael trust Bannister? Does he know about Michael's affair with Elsa? And who really killed Grisby?, Michael fakes a suicide bid, escapes from the courtroom, and there's a gripping climax in a Hall of Mirrors at an abandoned fun fair.