The opera opens in the forest near the dragon Fafner's lair. Siegfried, the son of Siegmund and Sieglinde, has been raised by the dwarf Mime, who plans to use him to kill Fafner and claim the ring for himself. Siegfried forges a new sword, Nothung, and sets off to find the dragon.
After a long and difficult journey, Siegfried reaches Fafner's lair. He tricks the dragon into revealing its weak spot and then slays it. As he drinks Fafner's blood, he gains the ability to understand the language of the birds. The birds tell him of the Valkyrie Brünnhilde, who is sleeping on a rock surrounded by fire.
Siegfried journeys to the top of the mountain and wakes Brünnhilde with a kiss. The two fall in love, and Siegfried vows to protect her. However, their happiness is short-lived. The wicked god Alberich, who created the ring, has been watching Siegfried and Brünnhilde. He plans to use Siegfried to get revenge on the gods.
Alberich disguises himself as a pilgrim and meets Siegfried. He tells Siegfried that Brünnhilde is unfaithful to him and that she is planning to betray him. Siegfried is heartbroken, and he leaves Brünnhilde. Alberich then appears to Brünnhilde and tells her that Siegfried is going to kill her. Brünnhilde is devastated, and she falls asleep in despair.
Siegfried returns to Mime, who tells him that he has poisoned Brünnhilde's drink. Siegfried is horrified, and he rushes back to Brünnhilde's rock. He finds her asleep and drinks the poisoned drink himself. Brünnhilde wakes up and finds Siegfried dying. She is overcome with grief, and she dies of a broken heart.
The gods gather on Valhalla, the home of the gods. They watch as the fire of Brünnhilde's funeral pyre consumes Walhalla. The world is destroyed, and the gods are powerless.