In the simmering hot summer of 1492, a monstrous evil is stirring within the Eternal City of Rome. The brutal murder of an alchemist sets off a desperate race to uncover the plot that threatens to extinguish the light of the Renaissance and plunge Europe back into medieval darkness. Determined to avenge the killing of her father, Francesca Giordano defies all convention to claim for herself the position of poisoner serving Cardinal Rodrigo Borgia, head of the most notorious and dangerous family in Italy. She becomes the confidante of Lucrezia Borgia and the lover of Cesare Borgia. At the same time, she is drawn to the young renegade monk who yearns to save her life and her soul. Navigating a web of treachery and deceit, Francesca pursues her father's killer from the depths of Rome's Jewish ghetto to the heights of the Vatican itself. In so doing, she sets the stage for the ultimate confrontation with ancient forces that will seek to use her darkest desires to achieve their own catastrophic ends.