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.

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.

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.