The three Norns, daughters of the earth goddess Erda, are busy weaving the rope of fate. Predicting Valhalla’s imminent fall, they notice that the rope of destiny is starting to fray and unravel. As the sisters try to make it taut, it snaps and they descend in terror to Erda. At dawn, Siegfried and Brünnhilde awaken from their night together. Though fearful that she may lose him, Brünnhilde encourages Siegfried to travel in search of heroic challenges. He gives her the ring as a pledge of his love.
In their home on the Rhine, Gunther, leader of the Gibichungs, and his sister Gutrune plot how to secure the Ring. Their halfbrother Hagen, son of Alberich, advises Gunther to marry Brünnhilde. By means of a magic potion, Siegfried could be induced to forget his vows and win her for Gunther in return for Gutrune’s hand. Siegfried’s horn call announces his approach. Gunther welcomes him, and Gutrune seals his fate by offering him the potion. He drinks and instantly forgets all about Brünnhilde and agrees to bring her to Gunther. On Brünnhilde’s rock, Waltraute visits her sister and tells her that she must yield the Ring to the Rhinemaidens or all is doomed. When she refuses, Waltraute departs in despair. Dusk falls as Siegfried appears, disguised as Gunther by means of the Tarnhelm. He wrests the ring from the terrified Brünnhilde and claims her as Gunther’s bride.
Alberich appears to Hagen and urges his sleeping son to win back the Ring from Siegfried. As dawn breaks, Siegfried returns and announces he has won Brünnhilde for Gunther. Hagen calls everyone to witness the joining of the two couples: Brünnhilde and Gunther, Siegfried and Gutrune. As they enter, Brünnhilde notices her ring on Siegfried’s finger. She deplores the trickery through which she was won and proclaims Siegfried to be her true husband. The hero, still under the potion’s spell, vows that he has never wronged the woman, and Brünnhilde angrily swears that he is lying. Bent on revenge, she reveals to Hagen the hero’s one vulnerable spot: a blade in his back will kill him. Taunted by Brünnhilde and lured by Hagen’s description of the Ring’s power, Gunther joins in the murder plot.
On the banks of the destroyed Rhine, the three Rhinemaidens bewail their lost treasure. Siegfried approaches and the maidens plead for the ring, but he ignores them. When Siegfried’s hunting party arrives, he describes his boyhood with Mime, the killing of Fafner, and finally—after Hagen gives him a potion to restore his memory—his wooing of Brünnhilde. Pretending indignation, Hagen plunges a spear into Siegfried’s back and the hero dies. At the Gibichung hall, Gutrune nervously awaits Siefried’s return. Hagen tells her that Siegfried has been slain by a wild boar, but the woman accuses Gunther of murder and Hagen admits the crime. Quarreling over the ring, Hagen kills Gunther but recoils in fear from the prize when the dead hero raises his arm. Brünnhilde appears and orders a funeral pyre built for Siegfried. Musing on the gods’ responsibility for his death, she returns the ring to the Rhinemaidens and walks into the pyre’s flames. As the world is consumed by fire, the Rhine overflows its banks and the Rhinemaidens, dragging Hagen to a watery grave, regain their treasure. Brünnhilde’s death frees the ring of its curse.