Set during the fall of the Roman Empire, 12 year-old Romulus Augustus (Thomas Sangster) has just become king and his rule lasts for a day before he and his teacher, Ambrosinus (Ben Kingsley), are captured and taken to the island fortress of Capri. Aurelius (Colin Firth), Romulus' personal guard, decides to save the emporer with a small group of his men and a Byzantine warrior, who turns out to be a woman called Mira (Aishwarya Rai). After the rescue, the group must travel to Britannia to find the legendary sword of Julius Caesar in order to save Rome.