Pretending to be Count Riario, Leonardo attempts to take over a ship, but Prince Alfonso of Naples, who knows Riario personally, exposes him. Leonardo and Zoroaster escape, but Alfonso takes the ship, which has a cargo of slaves. Leonardo invents a pedal-powered submarine in order to sneak under the ship unseen, while Amerigo Vespucci joins Alfonso on board. After nearly failing, Leonardo and Zoroaster get on board the ship with Amerigo's help. Lucrezia convinces Mercuri to enter the Castel Sant'Angelo to meet her father: the real Pope Sixtus IV. The false Sixtus seeks to isolate Florence by excommunicating the city.
