After an astrologer has foretold him he will die at an early age if he does not avoid a romantic entanglement, Alessandro Stradella, a well-known composer decides to leave Rome for the North of Italy. He takes advantage of his trip to visit Venice. On his way to the Doge`s City, he meets a beautiful, mysterious lady who immediately captivates him. Once in Venice he learns that the young lady`s name is Ortensia and that she is the daughter of a powerful man, Alvise Foscarini, in fact Venice`s chief inquisitor. Alessandro and Ortensia declare their love to each other and consider marrying, which infuriates Foscarini who does not want a "dissolute" artist in his family. Feeling the heat, the couple runs away from Venice. Having taken shelter in Torino, they are traced by the inquisitor, who pretending to feel remorse, has them return to Venice. But while they are on the road, Foscarini`s hired assassins murder Alessandro. As for Ortensia she is taken back to her father`s home by force.