Sigismondo, the courtier, mercenary, and sleuth who is as deft with his brains as he is with an ax, returns in this third tale of Renaissance Italy. Prince Scipione of Viverra is in danger: his vassal Carlotti has claimed the city of Mascia for his own, and the Pope is ready to give the Papal state to another if the Prince proves weak. Not only does the Prince need a victory, but he also needs to discover the Philosopher's Stone to make gold for his empty treasury. When Sigismondo arrives from Mascia he brings news of triumph - the Prince's condottiere, Ridolfo Ridolfi, has taken the city - but finds the Prince still in peril. Is it from those closest to him? Is his wife Isotta concealing an affair that threatens the Prince and his state? Does the hostage Donato Landucci want vengeance for his father's defeat? Has Ridolfi turned fickle? What about the mysterious alchemist, Doctor Vergilio or the celebrated holy friar Brother Ambrogio, who is using the people's fear of encroaching plague to preach sedition? Foul murder finally strikes, but who is poisoned and where will it lead? Sigismondo, accompanied, as always, by the shrewd halfwit Benno and Biondello the dog, is challenged time and again by those who would give poison to a prince...