A story, set in Rome of 44 A.D., concerning the amorous and political intrigues of the evil Empress Messalina, the wife of the Roman Emperor Claudius, and her eventual hounding to death.

In the prison of San Vittore there is, among other detainees, a strange type that they call "Il Cavaliere". The latter suffers a conviction for theft and his fellow prisoners have a certain respect for him.