At a cabaret, steel worker Dundee Reilly meets Mary Malone, sister of former boxing champion Pat Malone. When Mary is accosted by prizefighter Killer Agerra, Dundee knocks his rival unconscious. Under Pat's guidance, Dundee trains for a scheduled bout with Agerra. However, Dundee is framed for a shooting, and spends his prison term working in a quarry and developing his muscles. Following his release, Dundee substitutes for another fighter against Agerra. Acting on intuition, Mary informs Dundee that he was framed by his opponent, spurring him on to win in the final round.