ACT IThe celebration of Prince Siegfried's coming of age at the castle. The prince's mother gently scolds her son and reminds him that next day at the ball he has to choose his bride. Siegfried feels confused, he does not love anyone yet, he is sad about losing his freedom. Siegfried's mother to her son a present - an arbalest, and the Prince goes hunting.
On the shore of a lake. The kingdom of the evil magician Rothbart. White, proud swans, enchanted maidens, appear. Siegfried notices a beautiful swan. In the excitement of hunting he aims at the swan, but the swan suddenly turns into a girl. Odette, the beautiful stranger, reveals her secret to Siegfried: only self-denying love would have the power to destroy the evil magician and save Odette and the other maidens from his spell. Dawn is breaking - the maidens have to turn back into swans. Siegfried, fascinated by the beauty of Odette, swears eternal love to her.
A ball at the castle. Siegfried is dancing with the maidens, one of whom he has to choose for a bride. Suddenly a guest, unknown to anyone, arrives - this is the evil magician who has turned into a nobleman. He has brought his daughter, Odile, who is the very image of Odette, with him. Deluded by this similarity, Siegfried swears eternal love to Odile. The magician rejoices in his victory and disappears together with his daughter.
Again on the shore of the lake. Odette is despairing - Siegfried has broken his oath. Siegfried arrives. Odile has been only a vicious delusion. Odette and Siegfried are reunited.
A storm breaks out. Siegfried fights with the evil magician Rothbart. Odette tries to defend Siegfried and is wounded. Siegfried overpowers the magician, his castle collapses. The evil spell breaks - the love of Odette and Siegfried has won.