Tristan, having entirely recovered under her care, takes leave of the fair Ysolde, who has entirely lost her heart to him, and returns to Cornwall, where he relates his adventures, and speaks in such glowing terms of Ysolde’s beauty and goodness that the courtiers finally prevail upon the king to sue for her hand.

As the courtiers have tried to make the king believe that his nephew would fain keep him single lest he should have an heir, Tristan reluctantly accepts the commission to bear the king’s proposals and escort the bride to Cornwall.  Ysolde is of course overjoyed at his return, for she fancies he reciprocates her love; but when he makes his errand known, she proudly conceals her grief, and prepares to accompany the embassy to Cornwall, taking with her her faithful nurse, Brangeane.

The Queen of Ireland, another Ysolde, well versed in every magic art, then brews a mighty love potion, which she intrusts to Brangeane’s care, bidding her conceal it in her daughter’s medicine chest, and administer it to the royal bride and groom on their wedding night, to insure their future happiness by deep mutual love.

Wagner’s opera opens on shipboard, where Ysolde lies sullen and motionless under a tent, brooding over her sorrow and nursing her wrath against Tristan, who has further embittered her by treating her with the utmost reserve, and never once approaching her during the whole journey.  The call of the pilot floats over the sea, and Ysolde, roused from her abstraction, asks Brangeane where they are.  When she learns that the vessel is already within sight of Cornwall, where a new love awaits her, Ysolde gives vent to her despair, and openly regrets that she does not possess her mother’s power over the elements, as she would gladly conjure a storm which would engulf the vessel and set her free from a life she abhors.

Brangeane, alarmed at this outburst, vainly tries to comfort her, and as the vessel draws near the land she obeys Ysolde’s command and goes to summon Tristan into her presence.  Approaching the young hero, who is at the helm, the maid delivers her message, but Tristan refuses to comply, under pretext of best fulfilling his trust by steering the vessel safe to land:—­

   ’In every station
    Where I stand
    I serve with life and blood
    The pearl of womanhood:—­
    If I the rudder
    Rashly left,
    Who steer’d then safely the ship
    To good King Mark’s fair land?’

He further feigns to misunderstand the purport of her message, by assuring her that the discomforts of the journey will soon be over.  Kurvenal, his companion, incensed by Brangeane’s persistency, then makes a taunting speech to the effect that his master Tristan, the slayer of Morold, is not the vassal of any queen, and the nurse returns to the tent to report her failure.  Ysolde, however, has overheard Kurvenal’s speech, and when she learns that Tristan refuses to obey her summons, she comments bitterly upon his lack of gratitude for all her tender care, and confides to Brangeane how she spared him when he was ill and at her mercy.