An unlikely alliance is needed to save Italy from an Ottoman attack; Riario faces danger; Nico takes control of Vanessa's destiny.

Leonardo returns to learn that Duke Federico has been ruling Florence with an iron fist; a sinful Riario seeks redemption; King Ferrante negotiates with Lorenzo.

Entering the Vault of Heaven presents challenges for Leonardo and Riario; Lorenzo becomes a part of King Ferrante's bloody games; Lucrezia meets the Turk in Constantinople.

Leonardo and his allies face deadly threats as they search for the Book of Leaves; Carlo helps Clarice; the Sultan's son is intrigued by Lucrezia.

Leonardo uses his intellect to save Florence as Pope Sixtus brings powers together; Nico tries to resist Riario's temptations.

Leonardo makes an unexpected discovery in the New World. Lorenzo attempts to save Florence with the help of an old flame. Clarice struggles to retain control of the Medici Bank.

The Pazzis make their move; Leonardo gambles for the future of Florence; Riario makes progress in his quest for the Book of Leaves.

Leonardo and Riario face death; Zoroaster and Nico plan an escape; Lorenzo waits to meet with the king of Naples; Bayezid seeks diplomacy in Rome.

Leonardo continues his search for the Book of Leaves; Lorenzo is forced to make sacrifices when Pope Sixtus takes aggressive measures against Florence; Lucrezia looks for new alliances in Rome.

Leonardo attempts to navigate the Atlantic without maps; Lucrezia is smuggled into the Vatican for an important meeting; Lorenzo's identity is discovered during his trip to Naples.