The exiled Gualtiero, count of Montaldo, has been living a life of piracy pursued by his enemy Ernesto, duke of Caldara. Ernesto had forced Imogene into marriage (both men were in love with her) by threatening to injure her father.
Gualtiero is shipwrecked on the coast near Ernesto and Imogene's castle. He is recognized by Imogene when she offers food and shelter to the survivors.
Gualtiero and Imogene reaffirm their mutual devotion, but Gualtiero is unable to convince Imogene to leave her husband and their young child. Ernesto returns to hear his wife admit her love for his enemy.
In the subsequent duel Gualtiero kills Ernesto; he then surrenders and is sentenced to death. As he bids farewell, the despairing Imogene loses her mind.