Siegfried has grown up with the dwarf Mime, unaware of who his real parents are. Mime is in possession of the shards of Siegmund’s sword Notung, by they can only be forged anew by “he who fears nothing”. Valiant Siegfried succeeds in recasting the sword and leaves with Mime to claim the gold of the giant Fafner, who has taken the shape of a dragon. Mime plans to poison Siegfried as soon as they recover the treasure.
Mime’s brother Alberich also desires his gold and the ring back. Wotan appears in disguise as the Wanderer at Fafner’s cave, where Alberich is keeping vigil. Wotan tells Alberich about Siegfried’s quest and the dwarf warns Fafner. As Siegfried waits by the cave for the dragon to appear, he listens to the birds. He attempts to answer their song and wakes Fafner. Siegfried kills Fafner with his sword Notung and, upon tasting the dragon’s blood, suddenly understands the birds’ song. The birds advise him to take the Ring and the magic helmet Tarnhelm, and reveal Mime’s true intentions. Siegfried kills Mime, after which the woodbirds lead him to a mountain rock, where a sleeping figure lies surrounded by fire.
The Wanderer Wotan tries to block his path, but Siegfried breaks Wontan’s spear with his sword. Siegfried enters the ring of fire, finds Brünnhilde, and his feelings are stirred. He awakens her with a kiss from her enchanted sleep. Brünnhilde and Siegfried declare their love for each other, enraptured.
You can read the full synopsis and other background information in the programme booklet.