In San Francisco, policeman Lieutenant Riggs (Harold Huber) takes Mr. Moto, a detective and Lee Chan (Keye Luke), a student, to a prizefight between Bill Steele (Dick Baldwin) and Frank Stanton (Russ Clark), where the winner will take on the champion, Biff Moran (Ward Bond). However, the fight is fixed and gangster Nick Crowder (Douglas Fowley) bets big money that Stanton won't make it to the fifth round. He goes down in the fourth and dies shortly afterward.