A garden party for Siegfried's birthday
Prince Siegfried has just turned eighteen and his friend Alexander is throwing him a garden party as a surprise. The courtiers and local residents have all pitched in to help, but the prince's tutor, Von Rasposen, is displeased that Siegfried and Alexander are on such friendly terms with the peasants. The queen, Siegfried's mother, arrives and interrupts the festivities. She presents her son with a ring and reminds him of his duty to succeed her as monarch in the future. He will therefore have to choose a bride soon. Siegfried is overcome with grief at the prospect that his youth will soon come to an end. As night starts to fall, Siegfried discusses his future with Alexander. They decide to go on a ramble in the surrounding woods.
Siegfried and Alexander appear to be lost in the woods. They decide to rest for a while on the banks of a vast lake, but a large, circling bird of prey terrifies them. It is almost as if Von Rasposen has taken on another guise and continues to haunt them and spy on them. The bird is actually the evil sorcerer Von Rothbart. He summons a creature from the dark lake – it turns out to be a swan who then assumes a human form. Siegfried believes Odette, the swan queen and her flock, embody the ideals closest to his heart: sincerity and simplicity. Surrounded by so much purity and happiness, he vows to remain true to his ideals forever.
A formal reception is under way at the castle and several girls have been introduced to Siegfried as potential brides. Siegfried, however, refuses to choose a fiancée – much to the consternation of his mother and the astonishment of everyone else. But, Siegfried feels this display of pomp and circumstance stands in sharp contrast to the purity that he experienced at the lake. Von Rasposen announces the last guests: they are Von Rothbart, his daughter Odile and their entourage. Siegfried believes the black swan Odile is Odette, but is not completely sure. Von Rothbart and Odile then seduce him with a sensuous display of brilliance and virtuosity. To Alexander's dismay, Siegfried succumbs and offers Odile his ring. It is too late by the time Siegfried realises that he has betrayed his ideals and true love, Odette. In desperation, he rushes back to the lake.
The reconciliation with Odette
Disillusioned and feeling betrayed, Odette and her peers linger by the night lake, where Siegfried finds them. Odette forgives Siegfried and tries to comfort him, telling him he must learn to accept reality and live with it. Meanwhile, Von Rothbart tries to drive Siegfried away from the lake. Siegfried manages to defy him, but ends up drowning in the lake. When Von Rasposen returns from a futile search for the prince, Alexander finds the lifeless body of his friend. Siegfried's ideals will now live on in Alexander.