The invasion by King Charles of France and Della Rovere proceeds with victory seemingly inevitable as the French sack the city of Lucca and the Italian powers flee to their banner, with Lucrezia's husband Giovanni Sforza poised to join them in the name of Milan; inventor Leonardo Da Vinci (guest star John Lynch) shows his drawings and blueprints for war machinery to the invaders.

The invaders capture a fleeing and pregnant Lucrezia as they march on Rome, but she charms King Charles and is allowed to persuade her brother Juan to withdraw his hopelessly outmatched defensive troops; Pope Alexander VI awaits to learn of his fate as Charles enters the city and makes his way to the Vatican.

Abandoned by even his cardinals, Alexander meets King Charles with humility and saves his throne, even eliciting a confession from the conqueror he crowns as the new "King of France and Naples;" Della Rovere despairs as Charles abandons him; Lucrezia safely gives birth to a son in a convent as the Borgias secure an annulment of her marriage and plot revenge on their enemies.