Die Walküre ("The Valkyrie") is the second of the four operas that comprise Der Ring des Nibelungen (The Ring of the Nibelung), by Richard Wagner. It received its premiere at the Munich Court Theatre on 26 June 1870. It is the source of the famous piece "Ride of the Valkyries". Wagner took his tale from the Norse mythology told in the Volsunga saga.
It is worthwhile to understand that this act hinges on hidden identities that are known to the audience. (Wagner uses this situation in operas that are not part of the Ring: in the operas bearing their respective names, Parsifal does not know his own name, and his son Lohengrin is forbidden to reveal his.) The program tells even the first-time viewer the names of the characters, and, from his leitmotif and his covering his missing eye with his hat, the "stranger" or "old man" (described but not seen on stage) and Wotan (and Wolfe, and the Wanderer who will appear in Siegfried) can be recognized as one. Siegmund (whose name means "victory protector or shield") and Sieglinde (meaning "gentle victory") each withhold their own name until the act's climax. (It would appear that, unlike Parsifal, Siegmund knows his own name, though he is not the first to apply it to him.)
During a raging storm, Siegmund seeks shelter at the house of the warrior Hunding. Hunding is not present, and Siegmund is greeted by Sieglinde, Hunding's unhappy wife. Siegmund tells her that he is fleeing from enemies. After taking a drink of mead, he moves to leave, claiming to be cursed by misfortune. However, Sieglinde bids him to stay, saying that he can bring no misfortune to the "house where ill-luck lives."
Returning, Hunding reluctantly offers Siegmund the hospitality demanded by custom. Sieglinde, who is increasingly fascinated with the visitor, urges him to tell his tale. Siegmund describes returning home with his father one day, to find his mother dead and his twin sister abducted. He then wandered with his father, until parted from him as well. One day, he found a girl being forced into marriage and fought with the girl's relatives. However, his weapons were broken and the bride killed, and he was forced to flee to Hunding's home. Initially, Siegmund does not reveal his name, choosing to call himself 'Woeful'.
When Siegmund finishes, Hunding reveals that he is one of Siegmund's pursuers. He grants Siegmund a night's stay, but they are to do battle in the morning. Hunding leaves the room with Sieglinde, ignoring his wife's distress. Siegmund laments his misfortune, recalling his father's promise that he would find a sword in direst need. Sieglinde returns, having drugged Hunding's drink to send him into a deep sleep. She reveals that she was forced into a marriage with Hunding. During their wedding feast, an old man had appeared and plunged a sword into the trunk of the ash tree in the center of the room, which Hunding and his companions had all failed to remove. She expresses her longing for the hero who could draw the sword and save her. He expresses his love for her, which she reciprocates, and she begins to grope for where she recognizes him from, and then realizes she recalls his voice and that they resemble each other. When she learns from him the name of his father Wälse, she tells him that his name is Siegmund, and that the Wanderer left the sword for him.
Siegmund now easily draws the sword forth, and she tells him her own name, Sieglinde, and that they are siblings. He gives the blade the name "Nothung" (which evokes the dire need, for a weapon against Hunding, that it fills for him). He and Sieglinde flee together from Hunding's house.
Wotan is standing on a rocky mountainside with Brünnhilde, his Valkyrie daughter. He instructs Brünnhilde to protect Siegmund in his coming fight with Hunding. Fricka, Wotan's wife and the guardian of wedlock, arrives demanding punishment against Siegmund and Sieglinde, who have committed adultery and incest. She knows that Wotan, disguised as the mortal man Wälse, had fathered Siegmund and Sieglinde. Wotan protests that he requires a free hero (i.e. one that is not connected to him) to aid his plans, but Fricka retorts that Siegmund is not a free hero, but an unwitting pawn of Wotan. Backed into a corner, Wotan promises Fricka that Siegmund is to die.
Fricka leaves, leaving Brünnhilde with a despairing Wotan. Wotan explains his problems: troubled by the warning delivered by Erda (at the end of Das Rheingold), he had seduced the earth-goddess to learn more of the prophesied doom; Brünnhilde was born to him by Erda. He had raised Brünnhilde and eight other daughters as the Valkyries, warrior maidens who gather the souls of fallen heroes to form an army against Alberich. Valhalla's army will fail if Alberich wielded the Ring, which is in Fafner's possession. Using the Tarnhelm, the giant has transformed himself into a dragon, lurking in a forest with the Nibelung treasure. Wotan cannot wrest the Ring from Fafner, who is bound to him by contract; he needs a free hero to defeat Fafner in his stead. However, as Fricka pointed out, he can only create thralls (i.e. villeins, serfs, bondsmen, slaves) to himself. Bitterly, Wotan orders Brünnhilde to obey Fricka and ensure the death of his beloved child Siegmund.
Siegmund and Sieglinde enter the mountain pass, where Sieglinde faints in guilt and exhaustion. Brünnhilde approaches Siegmund, telling him of his impending death. Siegmund refuses to follow Brünnhilde to Valhalla when he finds out that Sieglinde cannot come along. Impressed by his courage, Brünnhilde relents and agrees to protect Siegmund instead.
Hunding arrives and attacks Siegmund. Blessed by Brünnhilde, Siegmund begins to overpower Hunding, but Wotan appears and shatters Nothung (Siegmund's sword) with his spear. Disarmed, Siegmund is slain by Hunding. Brünnhilde seizes Sieglinde and the shards of Nothung, and flees on horseback. Wotan looks down on Siegmund's body, grieving. He kills Hunding with a contemptuous gesture, and sets out in pursuit of Brünnhilde.
The other Valkyries assemble on the summit of a mountain, each with a dead hero in her saddlebag. They are astonished when Brünnhilde arrives with a living woman. She begs them to help, but they dare not defy Wotan. Brünnhilde decides to delay Wotan as Sieglinde flees. She also reveals that Sieglinde is pregnant by Siegmund, and names the unborn son Siegfried (meaning "joyous in victory" or "peace in victory").
Wotan arrives in wrath and passes judgement on Brünnhilde: she is to be stripped of her Valkyrie status and become mortal, to be held in a magic sleep on the mountain, prey to any man who happens by. Dismayed, the other Valkyries flee. Brünnhilde begs mercy of Wotan for herself, his favorite child. She recounts the courage of Siegmund and her decision to protect him, knowing that was Wotan's true desire. Wotan consents to her last request: to encircle the mountaintop with magic flame, which will deter all but the bravest of heroes (who, shown through the leitmotif, they both know will be the yet unborn Siegfried). Wotan lays Brünnhilde down on a rock and sends her into an enchanted sleep. He summons Loge (the Norse [half] god of fire) to create the magic fire to protect Brünnhilde, and Wotan departs in sorrow.