The forest. In the last lash of a storm, Siegmund, pursued by his enemies, staggers into a house built around a giant ash tree. Sieglinde enters, thinking her husband Hunding has returned, and sees the fugitive on her hearth. They sense an immediate attraction. She gives him water to drink and persuades him to stay. Hunding returns. While Sieglinde prepares the meal, Hunding asks Siegmund his story. It is revealed that those Siegmund has slain in battle were Hunding’s kin. For the moment Siegmund is protected by the laws of hospitality, but in the morning, Hunding says, they will fight to the death. Siegmund, left alone, longs for the sword his father Wälse had promised him. Sieglinde emerges; she has given Hunding a sleeping-potion. She points out to Siegmund the sword buried in the ash tree, telling him how on her wedding day an aged stranger thrust the sword into the tree, and no one since has been able to remove it. Siegmund promises to save her from her forced marriage. She recognizes him as her twin brother, and he claims her as his Wälsung bride. He joyfully draws forth the sword and they rush into the night.

A mountain pass. Wotan commands his warrior daughter Brünnhilde to protect Siegmund in his duel against Hunding. She runs off joyfully with her new commission. Wotan’s wife Fricka appears and, as the goddess of marriage, demands that he withdraw his protection of the incestuous lovers. Hunding must be avenged, and the twins must be punished, or the gods themselves will be subject to scorn. Wotan’s hope of having a Wälsung hero restore the Ring to the Rhinemaidens vanishes. He is impotent in the face of Alberich’s curse. Brünnhilde returns, and Wotan explains to her the history of the Ring. He mockingly blesses Alberich’s heir, through whom his own supremacy will come to an end; and he commands Brünnhilde to fight for Hunding. Brünnhilde is confounded.

Siegmund and Sieglinde are fleeing Hunding. Sieglinde is overtaken by terror and has a premonition of Siegmund’s death. She faints. Brünnhilde appears to Siegmund and promises to escort him to Valhalla among the heroes. Siegmund scorns the offer of Paradise if Sieglinde cannot accompany him. He threatens to kill Sieglinde on the spot rather than leave her to die at Hunding’s hands. Brünnhilde, deeply moved, resolves to disobey her father and fight for this hero who loves so ardently. Siegmund faces off with Hunding and aims a deadly blow, but Wotan appears and shatters Siegmund’s sword, leaving him to be killed by Hunding. Brünnhilde flees with Sieglinde and the fragments of the sword. Wotan contemptuously kills Hunding and vows to punish Brünnhilde.

The Valkyrie rock. The Valkyries assemble. Brünnhilde arrives with Sieglinde. She begs her sisters for help, but they are afraid to hide the woman from Wotan’s wrath. She bids Sieglinde seek refuge in the nearby forest, where the dragon Fafner guards the Rhinegold. Sieglinde refuses, wishing to follow Siegmund in death. Brünnhilde foretells to her the glorious prophecy that she will become the mother of Siegmund’s son Siegfried. Sieglinde thrills to the thought of the child she carries and rushes into the forest, taking with her the pieces of Nothung, Siegmund’s sword.

Wotan arrives, threatening the sisters when they beg him to spare Brünnhilde. They depart, and he is left alone with his best beloved daughter. Throwing herself at his feet, she reminds him that her actions conformed to his original intent. He will not be moved. A deep sleep shall come upon her, and she shall awaken a mortal, and prey to the first man who finds her. Brünnhilde begs him to encircle her with fire so that only a hero will be able to claim her–and she tells him of the hero who will soon be born. He kisses her eyes with sleep and mortality, then summons Loge, the god of fire; and soon her sleeping form is ringed with magic flames.