Venice, 1734. Castrato soprano Tito Amato, star of Venice opera, has let fame go to his head. Neglecting his vocal practice for dubious pleasures, Tito finds himself demoted to secondary roles and overshadowed by a visiting singer who usurps his position. But when the murder of scene painter Luca Cavalieri threatens to close the opera house, Tito sees an opportunity to reclaim his status and jumps at the chance to find the killer. He is aided by Englishman Augustus "Gussie" Rumbolt, who is in Europe making his grand tour. The hunt for the person who wears the mask of Palantinus carries Tito and Gussie into the treacherous depths of the city of Venice, dedicated as it is to masquerade and pleasure, where Tito matches wits with the masked leader of a secret society bent on the destruction of Venice's Jewish ghetto.