In 1858, a German princess, recently inducted into the convent of Sant'Ambrogio in Rome, wrote a frantic letter to her cousin, a confidant of the Pope, claiming that she feared for her life. A subsequent investigation by the Church's Inquisition uncovered the shocking secrets of a convent ruled by a beautiful young mistress, who coerced her novices into lesbian initiation rites and heresies, and who entered into an illicit relationship with a young theologian. Drawing upon written testimony and original documents discovered in a secret Vatican archive, is the never-before-told true story of how one woman was able to practice deception, heresy, seduction, and murder in the heart of the Catholic Church.