Based on the myth of King Arthur. A young, inexperienced squire Valiant, masquerading as Sir Gawain, is sent to accompany the Welsh princess Lady Ilene, a guest at Camelot, on her way back home. Little does he know that meanwhile, Arthur's wicked sister Morgan has retrieved a spellbook from Merlin's tomb and convinced the Viking warlord Sligon, ruler of the kingdom of Thule, to steal the magical sword Excalibur during a joust tournament. Valiant and the princess become part of the struggle of "he who holds the sword rules the world" which leads them both to love and Valiant to his princely destiny, as it turns out he is the rightful heir to the throne of Thule. The usurper is killed by his also evil brother Thagnar. During the final confrontation, with the help of Thule's ruler Boltar, Morgan is destroyed, Thagnar is slain, and Valiant rescues the princess and recovers Excalibur