Prizefighter Mason loses his opening fight so wife Rose leaves him for Hollywood. Without her around Mason trains and starts winning. Rose comes back and wants Mason to dump his manager Regan and replace him with her secret lover Lewis.

Kid Mason, a lightweight boxer managed by George Regan, ignores his trainer's advice and consequently loses a fight. Mason explains that he was desperate to earn money for his wife Rose, an ex-showgirl. When Rose learns Mason lost his bout, she leaves him in disgust to try for a career in Hollywood. Regan takes the distraught Mason and turns him into a champion, earning him the nickname of Iron Man. Now that Mason is successful, Rose returns and persuades him to take her back. Rose does her best to wean Mason away from his boxing friends, including Regan, who she knows to be her bitter enemy. Mason is too naive to realize that Rose has taken Paul Lewis, a theatrical producer, as her lover. She spends Mason's money lavishly and tries to turn him into a gentleman. When Regan catches Rose and Lewis together, Rose forces Mason to fire him and replace him with Lewis. Regan agrees to tear up Mason's contract on the condition that Mason fight his new boxer, Rattler O'Keefe, for the championship. On the night of the fight, Mason receives a letter from Mrs. Lewis which names Rose as the corespondent in her divorce. Mason is so despondent over the news that he loses the fight. Regan visits Mason's dressing room afterward and suggests that it was Rose who really defeated him. Finally finished with Rose, Mason renews his relationship with Regan.