In 1890s San Francisco, boxing is illegal. James J. Corbett (Errol Flynn), a brash young bank teller, attends a match with his friend Walter Lowrie (Jack Carson). When a police raid nets Judge Geary, a member of the board of directors of Corbett's bank, Corbett's fast talking gets his superior out of trouble. The judge is looking to improve the image of boxing by recruiting men from more respectable backgrounds and having them fight under the Marquess of Queensberry rules. He has even imported British coach Harry Watson (Rhys Williams (Welsh-American actor)) to evaluate prospects. Watson finds that Corbett, raised in a combative Irish immigrant family headed by Pat Corbett (Alan Hale, Sr.), has excellent fighting skills; Geary likes his protégé's seemingly-polished manner.