Sir Lancelot (Cornel Wilde) is a knight of the Round Table and one of King Arthur's (Brian Aherne) most trusted men. Arthur pledges to wed Princess Guinevere (Jean Wallace) and sends Lancelot to protect her on the long journey back to the castle. Arthur is unaware, however, that Guinevere and Lancelot have fallen deeply in love. As Lancelot struggles to reconcile his love for her with his duty to Arthur, he must also defend the land against a rival king.