During a naval battle in the South Pacific, Jimmy Weston is forced to strike a shipmate who has gone berserk. The sailor falls and is accidentally killed, and as a result of the incident, Jimmy's right arm becomes paralyzed. Navy doctors suggest boxing as a means to rehabilitate him and he becomes the Navy's middleweight champ. On discharge, Jimmy turns professional, over the objections of his girl friend, Navy nurse Sally Rivers, and trains with Doc Fuller. Tug Martin, a crooked manager, signs them both to a contract, and Jimmy easily wins a number of fights, becoming a big success. Tug and his girl friend, Birdie Bronson, then try to get Jimmy to throw his next fight but he refuses. As Tug has already bet a sizable sum that Jimmy will lose, he hires a punch-drunk, old fighter, Johnny Hart, as a sparring partner for Jimmy. During a workout, Jimmy knocks out Johnny and is later informed that he has killed him. Afraid to use his right hand, the one that killed the sailor and Johnny, Jimmy is defeated in his big fight, but signs for a rematch, intending to give his purse money to Johnny's family. However, when Sally finds no record of Johnny's funeral, she and Doc discover where Tug has hidden him and bring him to the arena just as Jimmy is taking a bad beating. When Jimmy sees Johnny, he realizes that he has been tricked and unleashes a terrific right cross that knocks out his opponent. As the police close in on Tug, Jimmy and Sally embrace.