Tito Amato returns from an operatic tour expecting to relax with his family. Instead he finds his merchant brother Alessandro imprisoned on a trumped-up smuggling charge, a capital crime in 1740 Venice. The senator who controls Alessandro's fate is determined to have a Venetian as the next pope. He forces Tito to Rome to sing at the villa of a powerful, music-loving cardinal who will control the coming papal election. Spying as he serenades Cardinal Fabiani and his guests, Tito peers into the dark mirror of Roman politics.

Pope Clement XII is sinking fast, and two candidates emerge as leading contenders for St. Peter's throne. Will Fabiani support the highborn Venetian whose secret passion is tinkering with electrical experiments or the humble cardinal with the gift of healing and a mysterious past? The discovery of a beautiful corpse in Fabiani's garden complicates Tito's mission. Fabiani believes that a member of his household killed the young maid in a fit of madness, but Tito — assisted by his irrepressible manservant Benito and Englishman Gussie Rumbolt — follows clues that indicate a more complex motive.

From the heights of the Janiculum Hill to the muddy waters of the Tiber, from a cozy Trastevere cookshop to the chilly corridors of the Quirinal Palace, the trio wrestles with events that could change the course of history. Can Tito stop the killer and affect the election before Pope Clement takes his last breath? Or will Alessandro face the scaffold?