Enredo

Cesare and Lucrezia, powerful 16th-century Italian siblings, rule together. Cesare wages war after committing a crime, while incestuously loving Lucrezia, who gets pregnant. He returns victorious, but the Pope separates the siblings.

In the early-16th century, the mighty Borgia family, Cesare Borgia and his pitiless sister Lucrezia rule all Italy. Cesare, incestuously in love with his sister, commits a crime and starts a war campaign in Romagna. Lucrezia, meanwhile, gets pregnant. Cesare returns victorious from the war, and the Pope is then forced to separate his two children.

In the late 15th century, Italy is boiling over with political intrigue amongst the many city states that comprise the region. The corrupt Rodrigo Lanzol Borgia is ensconced in Rome as Pope Alexander VI (1492-1503). While a cardinal, he fathered four children with Giovanna dei Cattanei, known as Vanozza: Juan; Cesare; Lucrezia; and Gioffre.

Daughter Lucrezia has been married to Giovanni Sforza, Duke of Pesaro, for a year -- but he allegedly has not consummated the marriage. Her family wants the marriage annulled, on the grounds of Giovanni's impotence -- a political move designed to weaken House Sforza of Milan. Ludovigo 'il Moro' Sforza is furious, and gives his nephew a chance to demonstrate his virility in front of the Milanese court, where he predictably fails. He's obliged to sign the annulment for Cardinal Sisto Borgia, the Pope's brother, which frees up Lucrezia to be conveniently married off to the House of Aragon.

Although Lucrezia is a willing player in family politics -- due in large part to her incestuous relationship with her father -- she's also coveted by her brothers Juan (the Duke of Candia) and the insanely jealous Cesare. Cesare discovers his brother's relationship with their sister, beats him to death in his private chambers, and blames his disappearance on House Sforza. His fathers spies, however, discover what really happened.

Lucrezia is betrothed to the youthful Alfonso, Prince of Aragon, just as Cesare secretly prepares to attack Caterina Sforza in Romagna (central Italy), hoping to divert attention away from his recent fratricide. Before he leaves, Cesare hopes to bed his sister, and sends his trusted lieutenant, Pierotto, to carry his passionate letters to Lucrezia. She's amenable to her brother's offer, but she's more amenable to his messenger, who proves to be more virile than her unlucky husband, Giovanni. So virile, in fact, that she soon finds herself pregnant.

As her marriage to Alfonso is about to take place, the hugely pregnant Lucrezia is presented to a shocked Papal Court. Lucrezia casually reveals that Pierotto is the father -- resulting in his immediate execution at the hands of an enraged Cesare.

Despite her condition, the marriage to Alfonso proceeds as planned, and the besotted Alfonso can't get enough of Lucrezia's fecund charms. However, Cesare's jealousy will not be deterred by marriage -- neither his, nor hers. When she and her beloved Alfonso return from Spoleto to Rome, Cesare's hired thugs attack Alfonso, but fail to kill him -- so he finishes the job himself.

Lucrezia finally resigns herself to her fate, and accepts her brother as her lover. In the director's final nod to historical accuracy, her father separates the siblings [marrying Lucrezia off to Alfonso I d'Este, Duke of Ferrara; and Cesare to Princess Charlotte d'Albret in France].