Young warrior Tristan kills Irish warrior Merholt to save his adopted homeland of Cornwall, England from ransacking. He allies with his Uncle, King Mark of Cornwall, at Tintagel Castle to bring back Irish Princess Isolde with permission from her mother, mystic, Queen Isolde, and father, African warrior, King Gurmon. Teenage Isolde is to wed Mark in a peacekeeping pact to protect both kingdoms from invasion. Isolde and Tristan have fallen in love and can?t admit it to themselves. This happened during Tristan?s earlier visit to Ireland while in disguise as the minstrel Tantris. When they unwittingly drink a truth potion thinking it is a sleep aid, this love becomes overwhelming. Tristan?s late mother Blanchefleur, King Mark?s sister, repeatedly visits the couple, and speaks her wisdom about the power of love and living one?s truth.
The lovers know they are in mortal jeopardy as they prepare for the wedding with their servants Governale and Brangoene. They meet secretly with the help of their aids, but are discovered by Ganelon, a jealous baron. King Mark learns of the betrayal . The couple, with Governal, flee into the wilderness. After some time has passed, Mark finds Isolde. He banishes Tristan and Governal while returning Isolde as his wife.
Heartbroken, Tristan returns to his birthplace in Brittany and engages in battle alongside the gallant warrior Kehedin. Tristan is wounded on the battlefield. He asks Kehedin to deliver a green stone ring to Isolde, a symbol of their love, and for Kehedin to marry Brangoene to fulfill his promise to find her a mate.
Governal takes Tristan home to his castle near the sea. Isolde does not reach him before his death. In longing, she dies upon his body. Mark finds the couple deceased and grieves. Kehedin begins to romance a frightened, defeated Brangoene.