Act One
An exhausted fugitive seeks refuge in a dismal home built around a mighty tree. Sieglinde tends to her unexpected visitor. When her husband Hunding arrives home, the stranger relates his sad tale: attempting to protect a young woman from an unwanted arranged marriage, he killed her brothers and was then forced to escape her avenging kinsmen. Hunding reveals that he had been part of the hunting party searching for the stranger. He offers the stranger shelter for the night, but advises him to prepare for a fight the next day.

Sieglinde drugs Hunding's drink so that the stranger can flee to safety. She, too, had been an unwilling bride and remembers that at her wedding, an unknown old man had thrust a sword deep into a tree trunk, but no man had the strength to pull it out. The stranger realizes that this must be the sword his father had promised him, and rejoices in reborn hope and newfound love for Sieglinde. Sieglinde recognizes him now as her long lost twin brother, Siegmund. In great excitement, Siegmund triumphantly pulls the sword from the tree and the two lovers run off into the night.

Act Two
Wotan, king of the gods, exhorts his daughter Brünnhilde, a Valkyrie (warrior maiden), to protect his mortal son Siegmund in his coming duel with Hunding. But Fricka, Wotan's wife and the protector of marriage, is outraged at the adulterous and incestuous love of Siegmund and Sieglinde, and forces Wotan to let Hunding triumph.

Wotan now tells Brünnhilde that she must let Siegmund die in combat. Wotan had been grooming Siegmund to be a "free hero"; a free-willed mortal unaided by the gods and the only one capable of regaining the cursed Ring of the Nibelung (guarded by the giant Fafner, who has since turned himself into a dragon) that Wotan was earlier forced to yield.

Siegmund and Sieglinde rest during their flight. While Sieglinde sleeps, Brünnhilde appears to Siegmund, instructing him to follow her to Valhalla after his death. But moved by his devotion to Sieglinde, Brünnhilde decides to disobey Wotan's orders and save Siegmund's life. After Hunding arrives and begins his battle with Siegmund, the furious Wotan appears and shatters Siegmund's sword. Hunding then easily kills Siegmund. Wotan then strikes him Hunding as well. Brünnhilde gathers up the broken sword pieces and leads Sieglinde to safety.

Act Three
Brünnhilde's eight sisters, the Valkyries, are on their way to Valhalla to report on the fallen heroes they have gathered. When Brünnhilde arrives with Sieglinde, the Valkyries refuse to hide them for fear of Wotan's wrath. Brünnhilde gives Sieglinde the broken sword pieces and sends her to seek refuge in the forest where the dragon Fafner hides, for Wotan will not follow her there. Sieglinde takes some comfort in the knowledge that she will bear Siegmund's son, whom Brünnhilde predicts will be the greatest of all heroes.

When Wotan arrives, he condemns Brünnhilde for her betrayal and sentences her to be stripped of her divinity and left asleep on the mountaintop, to be claimed by the first mortal man to awaken her. Brünnhilde begs Wotan to surround her with a ring of magic dire so that only the bravest of men would attempt to awaken her. Wotan relents, regretfully leaving his daughter to her long sleep, surrounded by terrifying flames.