Messalina (played by the stunning Betty Roland) is a power-hungry nymphomaniac who will do anything to become the Empress of Rome. She attracts Caligula's attention by fighting in the gladiator arena, and it is not long until she achieves her aim, upsetting Agrippina, the Emperor's younger sister, who hopes that her son Nero would one day become emperor. Agrippina successfully organizes the downfall of Caligula, but Messalina dampens her celebration by immediately engaging in sexual relations with his successor, Claudius. But naughty old Messalina is incapable of committing to a single man, and she shacks up with everyone in sight, including a hideous but well-endowed brothel patron, a saucy midget, her eunuch(!?!), and an ex-lover. When she becomes pregnant and it is clear that Claudius is not the father (as he has been away fighting in faraway places), Agrippina realizes that this is her chance to finally rid herself of her archenemy.