Count Arturo is engaged to Isoletta, but has fallen in love with a mysterious stranger who lives alone in the woods. The villagers think she is a witch. Arturo wants to run away with her, but the stranger refuses. Arturo’s friend Baron Valdeburgo tries to persuade him to go back to Isoletta. To elicit Valdeburgo’s sympathy for his plight, Arturo takes him to the stranger. To Arturo’s astonishment, the stranger and Valdeburgo greet one another with a tender embrace. The jealous Arturo immediately fights a duel with his friend, and Valdeburgo falls into the lake. The stranger’s cry of “You have killed my brother!” explains the affectionate greeting. Arturo plunges into the lake, leaving the despairing stranger alone with the bloodstained rapier. This is how the villagers find her, and they accuse her of murdering the two men. At the trial, both men reappear, still alive, thus proving the stranger’s innocence. Arturo still refuses to give up his passion for her. On the day of his wedding to Isoletta he runs away from the altar. When it emerges that the stranger is in fact the wife of the King of France and was forced to live in exile, Arturo stabs himself.