She directs Brangoena to mix a death-potion and invites him to drink
with her, but without her knowledge Brangoena has prepared a
love-potion, which inflames their passions beyond power of restraint.
Oblivious of the landing, the approach of the royal train, and all
that is going on about them, they remain folded in mutual embrace.

The second act opens in Cornwall, in a garden which leads to Isolde's
chamber, she being already wedded to King Mark. With Brangoena she is
waiting for Tristan. The King goes out upon a night hunt, and no
sooner has he disappeared than Isolde gives the signal for his
approach, while Brangoena goes to her station to watch. The second
scene is a most elaborate love-duet between the guilty pair, the two
voices at first joining ("Bist du mein? Hab'ich dich wieder?"). A
passionate dialogue ensues, and then the two voices join again ("O
sink' hernieder, Nacht der Liebe"). After a brief dialogue Brangoena's
warning voice is heard. Absorbed in each other, they pay no heed, and
once more they join in the very ecstasy of passion, so far as it can
be given musical form, in the finale of the duet, "O süsse Nacht!
Ew'ge Nacht! Hehr erhabne Liebes-Nacht." The treachery of Sir Melot,
Tristan's pretended friend, betrays the lovers to the King. Tristan
offers no explanations, but touched by the King's bitter reproaches
provokes Sir Melot to combat and allows himself to be mortally
wounded.

The third act opens in Brittany, whither Kurwenal, Tristan's faithful
henchman, has taken him. A shepherd lad watches from a neighboring
height to announce the appearance of a vessel, for Kurwenal has sent
for Isolde to heal his master's wound. At last the stirring strains of
the shepherd's pipe signal her coming. In his delirious joy Tristan
tears the bandages from his wounds, and has only strength enough left