The King of Northumbria is killed during a Viking raid led by the fearsome Ragnar Lodbrok (Ernest Borgnine). Because the king had died childless, his cousin Ælla of Northumbria (Frank Thring) takes the throne. The king's widow, however, is pregnant with what she knows is Ragnar's child because he had raped her during that fateful raid, and to protect the infant from her cousin-in-law's ambitions, she sends him off to Italy. By a twist of fate, the ship is intercepted by the Vikings, who are unaware of the child's kinship, and Thrall him.