Pursued by his enemies in the midst of a storm, the exhausted Siegmund takes refuge in the home of Sieglinde – a young woman coerced into marriage with the warrior Hunding. Through the tale he relates to his hosts, Siegmund describes himself, little by little, as the sworn enemy of Hunding; the latter nonetheless grants him hospitality for the night, but he will fight him the following day. As Hunding sleeps, Siegmund and Sieglinde feel an irresistible attraction to one another: as springtime gushes forth in the house, a torrid passion seizes the two heroes – an incestuous passion ... for the two are in reality brother and sister.
Siegmund and Sieglinde are the children of Wotan, born from his union with a mortal woman. In Wotan’s view, Siegmund represents the only way he can recover a magic ring that confers omnipotence; a ring that is now owned by a formidable dragon. Meanwhile, Fricka, Wotan’s scorned wife and the guardian of the laws of marriage, is unable to shut her eyes to the incestuous liaison of Siegmund and Sieglinde: she orders Wotan to put Siegmund to death. Himself incapable of destroying the fruit of his loins, the god calls upon his daughter, the Valkyrie Brünnhilde, to go and tell Siegmund of his imminent death.
The battle rages between Siegmund and Hunding. Against all expectations, although she is supposed to fell Siegmund in this mortal duel, Brünnhilde dares to disobey her father and protects Siegmund, forcing Wotan to intervene in person. Seized by a nameless rage against his daughter who has flouted his orders, Wotan immediately brings down Siegmund in combat and then, in a single stroke, brings down Hunding.He sets off to look for Brünnhilde, who has fled, to punish her.
The eight Valkyries, who are all virgins and immortal warriors, gather the bodies of fallen heroes and bring them to Valhalla, the home of the Gods, during a dizzying ride.
Brünnhilde confesses to her angry father: she has disobeyed him by protecting Siegmund, but did so out of love, thinking this was Wotan's true desire. The Valkyrie begs forgiveness, but the punishment has been decided: Brünnhilde will be stripped of her divine essence and become a mortal woman. Wotan immerses her in a magic sleep and encircles her with a ring of flames that will deter all but the bravest of heroes.