Tristan's ship is carrying Isolde, daughter of the Irish king, to Cornwall so that she can be married to its king, Marke. She is brooding and on edge. Tristan stays at his post, not speaking to her unless necessary. She tells Brangaene of her past history with Tristan. He came to her in disguise to be healed from wound he received I n combat with the Irish champion, Morold. Morold was Isolde's betrothed. As she cured his wound she realized who he really was and tried to strike him with a sword. When she looked into his eyes she was unable to kill him. Now he has come back to escort her to Cornwall to marry his uncle, the king. She hates him and her situation and decides the only way out is to kill both herself and Tristan with a poison draught. She tells her maid to prepare the potion and summon Tristan.
When he arrives they are both tense but still feel a mutual attraction. Brangaene cannot bring herself to prepare the death potion and substitutes a love potion instead. The two drink the potion and fall into each other's arms, finally declaring the love they have always felt for each other but were unable to express. The ship docks and King Marke arrives. Tristan and Isolde fulfill their roles but are dazed and mechanical. They meet passionately whenever they can find time to be alone. Eventually they are caught together by the king and his courtiers and exposed as lovers. Tristan does not try to defend himself when Melot challenges him and Tristan is mortally wounded. His companion Kurwenal spirits him away to his childhood home in Brittany, where he slowly dies of his wound. Isolde follows him by ship. As she arrives he dies in...