The pregnant Sieglinde finds refuge in the forest from the rage of the god Wotan. Shortly after giving birth to her son Siegfried, the progeny of her twin brother Siegmund, with the help of the Nibelung Mime, she dies. But just before her death she hands over to Mime the remnants of the sword Notung, which Wotan (now in the guise of a Wanderer) had once destroyed with his spear. Mime raises Siegfried in a cavern in the midst of the forest, in the hope that he would one day kill the giant Fafner, who in the shape of a huge dragon protects the Nibelung’s treasure with the ring, which gives unlimited power, and the Tarnhelm, and Mime could lay claim to the treasures for himself. However, Mime is unable to repair the sword Notung, the only weapon that could kill Fafner.
Wild cavern in the forest
Mime bemoans his fate: every sword that he forges for the strong Siegfried cannot withstand his power. Only Notung will do. But Mime is unable to restore the sword to its intact condition. Siegfried returns from the forest and gets into an argument with his unloved foster father, and asks him about his unknown origins. Under pressure, Mime admits the truth: that Siegfried’s mother died after his birth, while his father fell in combat. As evidence, Mime presents the fragments of Notung that he received from Sieglinde. Siegfried wants Mime to make a sword out of these pieces and then to strike out into the world. Excited by this idea, he storms from the cave. Left behind, Mime, increasingly despairing, is surprised by the Wanderer (Wotan). When Mime refuses to take him in as a guest, the Wanderer offers his head as the prize for a wager. The three questions Mime asks he can answer without difficulty. He then also challenges Mime: if he cannot also answer three riddles, he will have to die. Mime has no choice but to accept. The two first questions cause him no difficulties, but he is stumped by the third: who would be able to forge the sword Notung? The Wanderer answers his own question: he who was without fear. He refrains from taking Mime’s head, singing that his head belongs to he who knows no fear.
After the Wanderer leaves the cave, Mime has a horrific vision that the dragon Fafner is approaching him, and he cowers in fear. The returning Siegfried asks for the sword that Mime wanted to forge for him. Mime recognizes through the words of the Wanderer that he is doomed to lose to Siegfried unless he teaches him to fear. Siegfried, now curious, demands to learn fear, but beforehand seeks to forge his sword on his own. He begins to file the remains of the weapon and to melt the steel. Mime connives to murder Siegfried with the help of a poisoned drink to get the ring that grants unlimited powers after Fafner’s death. Siegfried forges the sword Notung and tests its sharpness for the first time.
Before the Neidhöhle, in which Fafner watches over the ring and the Nibelungen treasure, Alberich awaits the hero who can kill the dragon. The Wanderer who once stole the ring from Alberich appears. The two enemies recall past events. Alberich still demands the ring, considering himself the proper owner, while the Wanderer places his hope in Siegfried, who knows nothing of the ring and its powers. The Wanderer himself refrains from intervening, but warns Alberich of his brother Mime, who is seeking to use Siegfried for his own ends. In addition, he awakens the sleeping Fafner, so that Alberich warns of Siegfried’s danger and pleads with him to freely give up the ring. But Fafner is left unimpressed by the warnings.
The Wanderer leaves Alberich behind in fear and dread. Mime takes Siegfried to Neidhöhle and explains to him Fafner’s methods of battle. Siegfried is confident of his strength and agility and the power of Notung. Retreating from the scene (as Alberich did so earlier), Mime hopes that Siegfried and Fafner will kill one another. Siegfried, now alone, contemplates the forest and reflects about his background. His fails in his attempts to imitate the song of a forest bird, so instead he blows on his horn. The powerful sounds attract the attention of Fafner. Both seek a fight: Siegfried plunges the sword Notung through his heart. Dying, Fafner recounts the race of giant’s fate, a race which now has been utterly decimated with his death. Having unwittingly tasted dragon blood after submerging his hand in it, it becomes possible for Siegfried to understand the language of the forest bird. The bird advises him to secure the ring and the Tarnhelm.
While Siegfried is in the cave to get these objects, Mime and Alberich appear on the scene. Both lay claim to the treasures, especially the ring, and get caught up in an argument. The forest bird, who once again speaks to Siegfried, warns him of Mime’s duplicity and his murderous plans. When Mime tries to give Siegfried the poisoned drink, claiming it to be refreshment, he reveals his intent. Disgusted by the plans of his foster father, Siegfried chops off his head. He tosses the corpse into the cave blocked by the dead dragon. He hears the voice of the forest bird for a third time who shows him the path to the sleeping Brünnhilde. Siegfried follows him to the mountain of the Valkyries.
Wilderness at the foot of a rocky mountain
Erda, the mother of Brünnhilde and the prophetic Norns, is summoned from a long sleep by the Wanderer. He asks how the process that will inexorably lead to the demise of the gods can be slowed. Erda is not able to answer, and asks Wotan, who himself has done so much harm with his own deeds, to stop asking. The Wanderer puts Erda back to sleep; he says he voluntarily wants to surrender his power to Siegfried.
When he encounters Siegfried directly, he regrets his decision. Through constant questioning, he tries to stall him. Siegfried becomes increasingly impatient and shows an increasing lack of respect for the older man. Finally, the Wanderer threatens him with his spear that had already destroyed the sword Notung once before. Siegfried, happy to have found the enemy of his father, fights his way free. With a sword he destroys Wotan’s spear, the symbol of his power. The Wanderer cannot hold him back any longer; Siegfried storms through the blazing fire towards the apex of the Valkyrie mountain.
There he finds the sleeping Brünnhilde. He first thinks she is a man; only after removing her armor does he realize that it is a woman. With a kiss, he awakens her. After a long sleep, Brünnhilde happily greets the sun, light, and day. She recognizes Siegfried as the savior she had always believed in and whom she had foreseen. At the same time, she becomes aware that she is no longer a Valkyrie, but a mortal woman. For a long time, she resists Siegfried’s insistence, but is finally overcome with increasing passion. Together they sing an ode to their »glowing life« and »laughing death« with growing ecstasy.