The story centers on Larry Sloan, a boxer facing the daunting challenge of fighting Sven Vendenssen, "The Battling Swede," the heavyweight champion known for his towering size, strength, and agility. Larry, doubting his own chances against such a formidable opponent, receives encouragement from his sister Claire, who reminds him of their ancestral lineage to Brian Boru, the legendary Irish king who defeated the Vikings. Claire's words serve as a rallying cry for Larry to draw strength from his heritage.

As the match commences, Larry struggles to land any effective blows against Vendenssen, who dominates the early rounds with ease, playing with Larry rather than finishing the fight. However, a pivotal moment occurs when Larry, nearly defeated and on the verge of unconsciousness, experiences a vision. He sees a battle between Viking invaders, led by a giant resembling Vendenssen, and defenders led by a figure symbolizing Brian Boru. Inspired by the vision and his sister's encouragement, Larry miraculously finds the strength to fight back, eventually knocking out Vendenssen and winning the match, much to the astonishment of everyone, including himself.