Steve Harmer, once a promising heavyweight with a devastating right hook, faces a career decline due to his "paper jaw" – any hit to his chin results in a knockout. Despite his powerful punch, this weakness leads to multiple defeats, pushing him towards retirement. He returns to his Pacific Coast hometown, where he rekindles his relationship with Gloria Murken and learns of a fixed fight between Battling Rourke and Johnny Varelli, with heavy bets favoring Rourke.

Gloria reveals her brother has stolen money to bet on Varelli, unaware of the fix. Harmer devises a plan to save Gloria's brother from ruin by ensuring Rourke's defeat. He anonymously lures Varelli away on the fight night and takes his place in the ring, despite the crowd's disdain for Harmer's recent performances.

The fight against Rourke is brutal, with Harmer taking significant punishment but managing to stay in the fight. In a desperate final round, motivated by the thought of Gloria's brother's predicament and Gloria's distress, Harmer lands his signature right hook on Rourke, winning the fight but injuring himself in the process.