The three Norns spin the past, present and future into the Rope of Fate. They sing of Wotan felling the World Ash Tree and of Alberich’s curse. Their omniscience comes to a sudden end as the rope breaks.
On Brünnhilde’s mountaintop, Brünnhilde and Siegfried prepare to part. They exalt in their love and promises of fidelity. Siegfried gives Brünnhilde the Ring and sets off down the Rhine.
Gunther yearns for fame and asks his wily halfbrother, Hagen, for advice. Hagen points out that both Gunther and his sister remain unmarried and that Gunther should wed the greatest woman in the world (Brünnhilde). Gunther cannot woo her, however, but the hero Siegfried could on his behalf. Hagen produces a potion that can make Siegfried forget that he’s ever seen a woman and make him fall in love with Gutrune.
Siegfried is welcomed into Gibich Hall. He is offered a drink, tainted with the potion. He immediately declares his love for Gutrune, offers to help Gunther find a wife and swears a bloodbrother oath with his prospective brother-in-law. Gunther and Siegfried depart for Brünnhilde’s rock, leaving Hagen to keep watch.
Brünnhilde is visited by her Valkyrie sister, Waltraute. She has dared to incur Wotan’s wrath in order to tell her sister of the gods’ misery and to beg her to return the Ring to the Rhinemaidens. Only thus can she break its curse. Brünnhilde refuses to give up Siegfried’s pledge of love.
Brünnhilde hears Siegfried’s horn but is horrified to be confronted with a stranger. Siegfried has used the Tarnhelm to change his shape into that of Gunther. He claims Brünnhilde as Gunther’s bride, wrestles the Ring from her and they enter the cave together.
Hagen is visited by Alberich in the deepest part of the night. His father urges him to be strong, clever and to avenge him. Hagen pacifies him, saying that the plan is already in action.
Siegfried has sped back to claim Gutrune’s hand in marriage. Hagen is tasked with preparing for the double wedding and summons Gunther’s men. The bride and groom arrive and Brünnhilde is shocked to find Siegfried betrothed to Gutrune. She sees the Ring on his finger and realises what has happened. She accuses Siegfried of treachery, which he denies, and they both swear on Hagen’s weapon that they are telling the truth. Siegfried leaves with the bridal party.
Hagen offers to avenge Brünnhilde if she helps him defeat Siegfried. Her solution is simple: she used all her magic to protect him but left his back unguarded. Hagen tells Gunther that Siegfried has the Nibelung Ring and unites him with Brünnhilde in a pact to kill him.
The Rhinemaidens dream of a hero returning their gold to them. Siegfried is out hunting and comes across them. They offer to help him if he returns the Ring. He refuses their offer, and they tell him to watch out – he will die today and someone else will return the gold.
The rest of the hunting party arrive. To cheer up Gunther, Siegfried offers him wine and recounts tales from his life. The wine has been spiked by Hagen and he starts to recall his love for Brünnhilde. Hagen stabs him with the weapon he swore upon during the wedding. Siegfried dies thinking of Brünnhilde.
Hagen reveals Siegfried’s body to Gutrune, claiming that a boar killed him. Gunther, Gutrune and Hagen argue. In a struggle for the Ring, Hagen kills Gunther. Brünnhilde intervenes and takes ownership of both the Ring and Siegfried’s body. She demands a funeral pyre be built and meditates upon her loss. Finally, she bids Wotan eternal rest, tells the Rhinemaidens to reclaim the Ring from her ashes and rides into the flames on her horse, Grane.