Julius Caesar has chased his enemy and adversary Pompey to Egypt, beyond the borders of the Roman Empire. After a decisive battle on the banks of the Nile, Pompey flees into the hands of the Egyptians, only to be murdered at the command of Tolomeo, who rules Egypt alongside his sister Cleopatra. The two siblings are locked in a struggle for absolute power.
Pompey’s widow, Cornelia plots with Sesto, her son, to get their revenge on Tolomeo. Cleopatra seduces Caesar, eager to secure his support and tip the balance of power in her favour. Cornelia’s plot to murder Tolomeo is foiled and she and Sesto are arrested.
Tolomeo has ordered that Cornelia be sent to his harem but a new plot is devised to sneak Sesto in with her. Here he plans to kill Tolomeo when he is alone and unarmed. However, this second assassination attempt is also foiled, this time by Tolomeo’s general Achilla.
During a visit with Cleopatra, Cesare is ambushed by Tolomeo’s agents. Cleopatra implores him to flee but he decides to fight instead. Cleopatra suddenly realises that she has fallen in love. Open-conflict breaks out between Tolomeo’s army and the Romans. Overwhelmed in battle, Caesar leaps from a palace window in order to escape and is believed to have died.
General Achilla plans to defect but is attacked by Tolomeo before he can. Tolomeo’s army appears to have won the battle and Cleopatra mourns both her brother’s victory and Caesar’s death. But Caesar actually survived his fall from the palace window and comes across the dying Achilla, who gives Caesar his seal and the command of his army. Caesar vows to save both Cornelia and Cleopatra.
As the tide of battle turns, Tolomeo attempts to rape Cornelia, but Sesto appears and kills him. Caesar is victorious and declares Cleopatra queen of Egypt, promising to support her and her country.