Steve Costigan, the heavyweight champion of the Sea Girl, comes ashore in Los Angeles intending to enjoy some peace away from his usual brawls. Leaving his bulldog, Mike, on the ship, he explores the beach, where he meets and is enchanted by Marjory Harper, a beautiful young woman. After spending a pleasant day rowing and chatting with her, he promises to meet her again, despite witnessing her being scolded by a man named Bert for associating with sailors.

Ignoring Bert's warning, Marjory meets Costigan again, only to tell him they cannot see each other because of Bert, whom she describes as controlling and overbearing. Fueled by a mix of jealousy and protective instincts, Costigan heads to Hollywood to confront Bert, mistaking a movie star for him in a comical altercation.

Through his old acquaintance, Tommy Marks, Costigan learns of a movie being filmed that requires a boxer. Seeing an opportunity to legally fight and hoping to encounter Bert on set, he ends up inadvertently auditioning by beating up potential extras. He secures a role meant for Terry O’Rourke, who is injured, to play against Bert's double in the film, not knowing yet that Bert himself will be his opponent.

The fight scenes are filmed with authentic intensity, reflecting both Costigan's and Bert's capable boxing skills. Their rivalry escalates until Costigan, driven by his misconceptions of Bert's relationship with Marjory and a personal vendetta, knocks Bert out, disrupting the film's intended climax. It’s only after this intense showdown that Costigan learns from Tommy that Bert is actually Marjory's brother, not her suitor, leaving him embarrassed and regretful over his actions.