In 1758 in the church of San Lorenzo in Naples where Vincentio di Vivaldi sees the beautiful Ellena di Rosalba with her aunt, Signora Bianchi. Vivaldi is struck with her beauty, and intends to court her, with the hopes that they will end up married. When Vivaldi's mother, the proud Marchesa, hears about his love for a poor orphan, she appeals to her ambitious and cunning confessor, Father Schedoni, to prevent the marriage, with a promise that she will help him obtain promotion in his order. As Vivaldi continues to visit Signora Bianchi at Villa Altieri, he is approached by a monk, who seems to be an apparition, threatening him to keep away from the villa and Ellena. After each encounter, Vivaldi tries in vain to capture the strange monk, with the help of his friend Bonarmo and his faithful servant Paulo.