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 builds an underwater suit and uses the sewers to enter the Vatican, where he meets the Pope and the mysterious prisoner. Giuliano reveals the true identity of Rome's spy.

The Pazzis prepare a murderous plot for Easter Sunday. The Turk tells Leonardo where to find the Book of Leaves. Lucrezia makes a confession as Leonardo attempts to save the Medicis.

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 quest for the Book of Leaves. The Pope’s nephew arrives and meets his spy. Leonardo’s war designs fail, causing a rift with the Medicis. The Pope learns of Leonardo’s prowess.

Lorenzo orders Piero da Vinci to defend his estranged son in court. During a performance for visiting royalty, Leonardo surprises the corrupt judge. Back at his workshop, Leonardo is surprised by the Turk.

Leonardo and his allies are forced to retreat when the Ottoman Empire storms the city of Otranto.

Riario engages the Pope and a mysterious prisoner in a discussion concerning the count's defeat, while Leonardo searches for a rational explanation when an outbreak of demonic possession occurs at a convent, and the blame is placed on the Medicis.

Bechhi is accused of being a spy for Rome. The armies of Rome and Florence face off, and Leonardo reveals his latest weapon.

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.

Leo and Sophia struggle to control the mysterious device they've built. Back in Florence, Riario awaits judgment while Lorenzo and Vanessa take their partnership to the next level.

Nico and Zoroastre turn to an old enemy to gain support for the Crusade. Leo is ambushed by the Labyrinth.

A clue from the Turk about the Book of Leaves sends Leonardo to Wallachia, where he encounters Vlad Dracula. Lorenzo and Piero meet the Duke of Urbino. The search for the true spy continues.

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.

A former nemesis returns to Florence and stands in opposition to Crusade efforts. Vanessa and Nico ponder their futures; Leo attempts to decipher the Turkish armor.

Leo must put his faith in his friends and in himself to have a chance to defeat the Turks.

Rising artisan Leonardo da Vinci is commissioned by the powerful Medici to create an Easter spectacle in Florence. After some maneuvering, da Vinci is hired to engineer war machines. A mysterious Turk intrigues Leonardo.

Leo devises an escape from Otranto but may not be able to save those closest to him.

Leonardo investigates a horrific murder that may result in the Labyrinth being exposed.