Soon after this, peace was declared between the two countries; and as the crowning pledge of the truce, King Mark was persuaded by his knights to ask the hand of the Princess Isolda in marriage. Tristan joined heartily in pressing forward this plan; for, believing that Isolda was now lost to him, he felt that he could reward her best for her kindness to him by making her Queen of Cornwall.
But King Mark was growing old, and, being childless, had decided to make Tristan his heir: and it was not until his beloved nephew himself added his entreaties to the desires of the courtiers that he at length gave consent. Then, when peace and friendship had been sworn by both nations, and the King of Ireland had willingly agreed to bestow his daughter upon King Mark as the pledge of their truce, Tristan was despatched in a gilded barge to conduct the lovely bride to her new home.
Isolda submitted to her father's will with due filial obedience and reverence; but her heart was filled with scorn and hot anger against the brave knight she had nursed back to life and health. As she now reclined in her curtained recess within the stately vessel that bore her so swiftly away from her native land, she declared passionately to her attendant handmaid, Brangæna, that she had been betrayed by Tristan; for after vowing fealty to her in Ireland, he had but returned to demand her in marriage for his kinsman. Brangæna, alarmed at this outburst, attempted to sooth her mistress's angry feelings by assuring her that Sir Tristan had doubtless meant to show his gratitude by making her Queen of Cornwall; and she added that King Mark, though advancing in years, was good and noble in disposition, and worthy of admiration and regard.
But Isolda gazed impatiently beyond the curtains at the silent, motionless figure of Tristan, wondering sadly how she could support a loveless life so near that glorious knight, who now seemed so indifferent to her; for Tristan, struggling to repress the love in his heart, had kept sternly aloof from his fair charge throughout the voyage, fearing to trust himself in her presence. This seeming unkindness and studied coldness enraged the proud and unhappy princess to such a pitch that she determined they should die together before landing in Cornwall; and she sent Brangæna to the helm to command Tristan's immediate presence in her recess.
At first Tristan refused to leave the helm, remembering his duty and loyalty to his royal uncle; but when, just as they were approaching the shore, Isolda sent another message, imperiously declaring that she would not land in Cornwall unless he sought her pardon first, the trembling knight was forced to yield to her request.
Isolda meanwhile opened her casket of drugs and simples, saying she desired a potion that would cure her of all her woes; and selecting a phial containing a deadly poison, she bade Brangæna pour it out into a golden cup.
But Brangæna was horror-struck; and, determined to save her beloved mistress from the consequences of so rash a resolve, she poured away the poison, unseen by Isolda, and filled the golden cup instead with a love-philtre that the Queen of Ireland, skilled in sorcery, had placed in the casket for her daughter to drink with her husband on her wedding-night.
When Tristan appeared within the recess, Isolda began to pour forth bitter words of reproach upon him, declaring that though she had preserved his life when he lay in feebleness before her, she had still sworn vengeance upon him; and then, offering him the golden cup, she bade him drink its contents with her as a final truce to all their strife. The ship was by this time at the landing-stage, where King Mark already stood with his lords, waiting to receive the lovely bride; and, full of despair, Tristan took the proffered cup and began to drink.
When he had swallowed half the draught, Isolda snatched the goblet from his trembling hand and drank the remainder; and then the two stood and gazed into each other's eyes in wonder and bewilderment. For the strange potion was coursing wildly through their veins like a fiery stream, changing all their dull despair into the glow of passion, and filling their hearts with uncontrollable love and desire for each other; and at last, utterly powerless to fight against the ecstasy within them, they fell into each other's arms, overcome by a rapture they could not quell.
Brangæna, terror-stricken at the dire result of her fond deed, implored the lovers to recollect their duty and the scene that was going on around them, for all their lords and attendants were now waiting for Tristan to conduct his royal charge to King Mark.