As a fight is now imminent between Siegmund, his mortal son, and Hunding, Wotan, who is up on a rocky mountain overlooking the earth, summons Brunhilde the Walkyrie to his side, bidding her saddle her steed and so direct the battle that Siegmund may remain victor and Hunding only fall. Chanting her Walkyrie war-cry, Brunhilde departs, laughingly calling out to Wotan that he had best be prepared for a call from his wife, who is hastening toward him as fast as her rams can draw her brazen chariot. Brunhilde has scarcely passed out of sight when Fricka comes upon the scene. After upbraiding Wotan for forsaking her to woo the goddess Erda and a mortal maiden, she says that, as father of the gods and ruler of the world, he is bound to uphold religion and morality. She then dwells angrily upon the immorality of the just consummated union between Siegmund and Sieglinde, who are brother and sister, and finally forces her husband, much against his will, to promise he will revoke his decree, give the victory to the injured husband, Hunding, and punish Siegmund, the seducer, by immediate death.
Wotan therefore summons Brunhilde once more, and sadly bids her to shield Hunding in the coming fight. Brunhilde, who realizes that the second command has been dictated by Fricka, implores him to confide his troubles to her. She then hears with dismay an account of the way in which Wotan has been beguiled into wrongdoing by Loge, of his attempts to gather an army large enough to oppose to his foes when the last day should come, and of his long cherished hope that Siegmund would recover the fatal ring which he feared would again fall into the revengeful Alberich's hands. Finally, however, Wotan repeats his order to her to befriend Hunding, and Brunhilde, awed by his despair, slowly departs to fulfil his commands.
The god has just vanished amid the mutterings of thunder, expressive of his wrath if any one dare to disobey his behests, when Siegmund and Sieglinde suddenly appear upon the mountain side. They are fleeing from Hunding, and Sieglinde, who has discovered when too late that Siegmund is her brother, is so torn by remorse, love, and fear that she soon sinks fainting to the ground. Siegmund, alarmed, bends over her, but, having ascertained that she has only fainted, makes no effort to revive her, deeming it better that she should remain unconscious during the encounter which must soon take place, for the horn of the pursuing Hunding is already heard in the distance.
Siegmund has just pressed a tender kiss upon Sieglinde's fair forehead, when Brunhilde, the Walkyrie, suddenly appears before him, and solemnly warns him of his coming defeat and death. He proudly tells her of his matchless sword, but she informs him that his reliance upon it is quite misplaced, for it will be wrenched from his grasp when his need is greatest. Then she tries to comfort him by describing the glory which awaits him in Walhalla, whither she will convey him after death.
Siegmund eagerly questions her, but, learning that Sieglinde can never be admitted within its shining portals, passionately declares he cannot leave her. He next proposes to kill her and himself, so that they may be together in Hela's dark abode, for he will accept no joys which she cannot share:—
‘Then greet for me Valhall,
Greet for me Wotan;
Hail unto Wälse,
And all the heroes!
Greet, too, the graceful
Warlike mist-maidens:
For now I follow thee not.’
Brunhilde's heart is so touched by his love for and utter devotion to Sieglinde, and she is so anxious at the same time to fulfil Wotan's real wish, in defiance of his orders, that she finally allows compassion to get the better of her reason, and impulsively promises Siegmund that she will protect him in the coming fray. At the same moment Hunding's horn is heard, and Brunhilde disappears, while the scene darkens with the rapid approach of a thunderstorm. Such is the darkness that Siegmund, who has sprung down the path in his eagerness to meet his foe, misses his way, while Sieglinde slowly rouses from her swoon, muttering of the days of her happy childhood when she dwelt with her family in the great wood. Suddenly, the lightning flashes, and Hunding and Siegmund, meeting upon a ridge, begin fighting, in spite of Sieglinde's frantic cries.
As the struggle begins, Brunhilde, true to her promise, hovers over the combatants, holding her shield over Siegmund and warding off every dangerous blow, while Sieglinde gazes in speechless terror upon the combatants.
But in the very midst of the fray, when Siegmund is about to pierce Hunding's heart with his glittering sword, Wotan suddenly appears, and, extending his sacred spear to parry the blow, he shivers the sword Nothung to pieces. Hunding basely takes advantage of this accident to slay his defenceless foe, while Brunhilde, fearing Wotan's wrath and Hunding's cruelty, catches up the fainting Sieglinde and bears her rapidly away upon her fleet-footed steed.
After gazing for a moment in speechless sorrow at his lifeless favourite, Wotan turns a wrathful glance upon the treacherous Hunding, who, unable to endure the divine accusation of his unflinching gaze, falls lifeless to the ground. Then the god mounts his steed, and rides off on the wings of the storm in pursuit of the disobedient Walkyrie, whom he is obliged to punish severely for his oath's sake.