Act I: The Royal Hunting Ground
It is Siegfried’s birthday. A buoyant, carefree air prevails, as the Prince’s knights return from a successful hunt and are greeted by the Court Fool, accompanied by a serving Wench. With Siegfried’s arrival, the knights perform a swaggering, boisterous dance intended to honour their Prince. Siegfried's mood, however, is less than receptive to their antics and, although he tries to conceal his indifference, it is clear the Prince does not feel wholly at ease in this world.
The Queen enters in a ceremonial procession and expresses to Siegfried her wish that he marry. Her insistence, however, only serves to deepen the Prince’s melancholy and reinforce the sense of estrangement he feels from court society. His friend, Benno, attempts to raise his spirits in a series of lighthearted dances with the Fool and the Wench, but they have little effect. Benno's efforts are followed by more dances involving the knights and the Wench, which begin as mere diversions, but grow increasingly unsettling and violent.
When Benno sees a flight of swans, he urges Siegfried to follow him so that they might hunt the birds. Eager to escape the brutality and unpleasantness of the court, the Prince leaves with Benno.
Act II: The Marsh
Pursuing the swans, Siegfried is separated from Benno and finds himself alone in a mist-laden marsh. He encounters Rothbart, the menacing figure from the Prologue, now in an earthly guise. Rothbart initially threatens Siegfried, but suddenly changes his demeanour by tempting him with a beautiful swan, Odette. Siegfried is captivated by the swan’s radiant and unearthly beauty and, as other swans join them in a series of dances amid the marsh's twilit landscape, he and Odette fall in love. As they profess their love, however, Rothbart intervenes and they must part.
Act III: The Ballroom
Amid the regal opulence of the court, Siegfried awaits the presentation of four foreign princesses, one of whom he must choose as his bride. One after another, the princesses are brought forward and unveiled by their respective ambassadors before Siegfried. The princesses, Hungarian, Russian, Spanish and Italian, all dance for Siegfried, hoping to win his approval and love, but none is successful.
Suddenly Rothbart appears. With him is another princess, a mysterious figure in black named Odile. Siegfried believes Odile to be none other than his beloved Odette and after she dances for him, he chooses her to be his wife. This unwitting betrayal of Odette brings catastrophe upon the court, which is engulfed in a flood. Siegfried is the only one to survive.
Act IV: The Lakeside
Having fled the destruction of the court, Siegfried seeks refuge by the lakeside. There, Odette appears to him, in the company of other swans. Odette forgives Siegfried for his betrayal and the promise of reconciliation shines momentarily, but Rothbart appears once again to separate the lovers. He summons forth a violent storm that scatters all in its path. Rothbart and Siegfried struggle. When the storm subsides, Odette is left alone to mourn the dead Siegfried.
— John Reardon