The Doge attends a nightly ball to celebrate the betrothal of his son Manrico with Lady Isabella Fiesci and his appointment as ambassador at the royal court of France.

Manrico, a patriot and soldier at heart, is not delighted about this arranged marriage, and Gualtiero, his uncle and the Doge's brother-in-law, supports him against his father's opinion.

The party is suddenly raided by a gang of Skokian pirates led by Titta and his mate Rossana, who strip the guests of their valuables.

Manrico, who has fallen in love with Rossana, persuades Ostenburg to entrust her to his supervision, and then releases her, which wins him her affection.

To forestall her punishment for piracy by the Doge, Gualtiero adopts Rossana as his daughter, thus allowing her and Manrico to get married.