In 64 A.D., Marcus Superbus is Prefect of Rome. When the Emperor Nero decides to renew persecution of the Christians, Marcus opposes him, fearing for the safety of Mercia, the Christian woman whom he loves. Through the machinations of the Empress Poppaea and other women at court, Tigellinus, Nero's agent in the war against the Christians, convinces Nero to have Mercia arrested. Marcus appeals to the emperor for mercy, but is told that she can be saved only by renouncing Christianity. Waiting to enter the arena to be killed, Mercia steadfastly refuses to reject her religion, despite Marcus' pleas. Finally, Marcus is converted by her and they enter the arena to face death together.

At a dance given by Earl Dexter, his wife, for the gratification of a whim, wears a beautiful pearl necklace recently purchased by Viscount Acheson. Craig Dare, who is a gentleman thief, makes love to Earl Dexter's wife, and at the same time succeeds in stealing from her the pearl necklace and handing it out of the window of the house to Tony Oscaros, a chauffeur, who is none other than Dexter, who is leading a dual life.