Prince Siegfried, a young royal celebrating his coming of age, encounters a crowned swan during a hunt near an enchanted lake. When his friend Adolf tries to shoot the swan, the sorcerer Rothbart transforms Adolf into stone. Siegfried follows the swan and witnesses its transformation into Princess Odette. She reveals Rothbart's curse: she lives as a swan by day, and only a vow of true love can break the spell.

Siegfried feels an instant connection to Odette, even in her swan form, drawn by her eyes. He invites her to his birthday ball the next evening, determined to choose her as his bride. Despite Odette's reluctance due to Rothbart's control, Siegfried persuades her to attend. He returns to the palace burdened by his mother's expectation to select a bride from visiting princesses but resolves to marry only Odette.

At the ball, Siegfried rejects the princesses presented to him. Rothbart's daughter Odile arrives disguised as Odette through enchantment, deceiving Siegfried. He pledges his love and marriage to her. The real Odette, having escaped Rothbart's castle with the help of squirrels Hans and Margarita, witnesses the vow but is captured by Rothbart before she can intervene. Rothbart reveals the deception and Odile reverts to her true form, showing Siegfried his error.

Siegfried pursues Rothbart and Odile to their castle. During the confrontation, Rothbart disarms Siegfried and threatens his life. To save Siegfried, Odette offers to marry Rothbart. Unwilling to let her remain captive, Siegfried seizes Rothbart's sword and impales himself. This self-sacrifice triggers a surge of light that destroys Rothbart and Odile, undoing all of Rothbart's curses. The castle collapses, Adolf reverts to human form, and Odette's curse breaks. Siegfried survives and reunites with Odette.