As Conqueror Julius Caesar is drawing his last breath, he swears Tyrannus—Rome's finest warrior—to an oath to protect his successor, Octavius, his 18-year-old nephew. Tyrannus and Octavius are forced into exile to protect the young man from those who want to sever Caesar's bloodline once and for all.

Befriended by aristocrat Sebastian Flyte, Oxford student Charles Ryder finds that the power and privilege experienced by the family is seductive. On a visit to the ancestral home, Brideshead, he falls in love with his friend's sister, Julia. However, as his ties to the Flytes deepen, Ryder finds himself at odds with their strong Roman Catholicism.