Tristam of Cornwall defeats an Irish messenger demanding tribute, but is wounded in the effort. Put out to sea to die, he washes up on the Irish coast and is nursed by Isolda, daughter of the Irish king, who falls in love with him. Tristam sails by to Cornwall only to have to return to Ireland to bring Isolda back as bride for his uncle, King Mark. She reluctantly marries Mark, but her love for Tristam only grows, and the two run away. Caught, they are forgiven by Mark once Isolda proves her chastity by an ordeal of fire. Tristam sets sail and meets Yolande, daughter of the Duke of Brittany, who falls in love with him. Her lover mortally wounds Tristam who sends for Isolda. She arrives too late and dies in despair.