1489—When Giulia Farnese came to Rome to make an arranged marriage with young noble Orsino Orsini, she dreamed of learning and power in the glittering city of the Renaissance popes. However, her mother-in-law seems frightened, and her husband refuses to consummate the marriage at the direction of the head of his family, Lord Bracciano. But Giulia herself has a secret: she sees visions in mirrors and hears the whispers of spirits, the gifts of an ancient sibyl in an age when magic is heresy punishable by death. Is this ability the reason Bracciano has trapped her in this sham of a marriage? As she struggles to unearth answers, Giulia finds herself drawn to her mother-in-law's cousin, Cardinal Rodrigo Borgia. Ruthless, sophisticated, and old enough to be Giulia's father, Rodrigo is a humanist, a collector of pagan art and heretical writings, and a loving father to his illegitimate children. He is a bright spot in Giulia's chilly life—but to Bracciano, he's a political rival to be removed. Bracciano's dark rites to summon demons may make Giulia the instrument of Rodrigo's destruction. Dealing with demons is a mortal sin. Refusing Bracciano would be a fatal mistake. And Giulia’s growing attraction to Rodrigo might be her downfall—or the key to her salvation. To defy the demon's power and seize control of her life, Giulia will need to cross the line between innocence and dangerous knowledge. And once she's descended into that underworld, she is not coming back unchanged.

1492: Giulia Farnese is the mistress of the powerful Cardinal Rodrigo Borgia. Educated, brave and ambitious, Giulia revels in the art and ideas of the Renaissance and in her newfound influence as the consort of one of the leaders of the humanist movement within the Vatican. The gifts of prophecy and magic that made her a weapon against Rodrigo but allowed her to save his life are gone with her virginity—or so she thinks. Now the pope is dying, plunging Rome into lawless chaos until a new pope can be elected. The most likely candidates want to purge Rome of heresy, endangering both Giulia's friends and the fragile Renaissance itself. A dark horse candidate who most people underestimate to their peril, Rodrigo is ruthless and clever; but to seize the ultimate prize of the papacy, he'll need all the help he can get. He relies on Giulia to be his eyes and ears in the world of powerful women and to negotiate on his behalf when the voting cardinals are locked in seclusion. Drawn into a high-stakes game of bribery and bargains, Giulia discovers all too soon that losing means paying a deadly price. Her only hope of protecting those she cares about from Rodrigo's enemies lies in mastering the magical gifts she once thought lost. For Giulia to claim the divine power of a pagan priestess may be the ultimate heresy—or a way to win her lover the papal crown.