Princess Rossana, also known as Odette, endured three years of captivity after her kidnapping by the sorcerer Rothbart, who demanded her hand in marriage. Upon her refusal, he cursed her to become a swan by daylight, only regaining her human form each night. This cycle would persist until a man pledged his true and complete love, breaking Rothbart's power.

Prince Siegfried first encountered her as a crowned swan upon a lake. At nightfall, as she transformed, fear gripped her and she urged Siegfried to flee for his safety. He persisted, compelling her to reveal her identity and the curse. Rossana confessed she had secretly loved Siegfried since her captivity began, long before their meeting.

Rothbart imprisoned her within his castle to prevent her attendance at Siegfried's birthday ball. With aid from two squirrels, Hans and Margarita, Rossana escaped, demonstrating resourcefulness and defiance. She raced to the ball to warn Siegfried.

During the festivities, Rothbart restrained Rossana, forcing her to watch as Siegfried declared his love for Odile – Rothbart's daughter magically disguised as Rossana. This cruel deception plunged Rossana into despair, causing her to faint. Once Siegfried realized the trick, he pursued Rothbart and Odile back to their castle.

Cornered by Rothbart in the ensuing fight, Siegfried faced death. To save him, Rossana offered to marry Rothbart. Siegfried, however, chose sacrifice, impaling himself upon Rothbart's sword. This act triggered a magical explosion that obliterated Rothbart and Odile, destroyed the castle, and shattered all Rothbart's enchantments.

Siegfried's sacrifice lifted Rossana's curse. She survived the castle's collapse and reunited with Siegfried, whose love had restored her permanent human form. His ultimate act fulfilled the condition to break the spell. The restoration extended to all others Rothbart had enchanted, including the squirrels Hans and Margarita.