The story picks up at the point where The Robe ends, following the martyrdom of Diana and Marcellus. Christ s robe is conveyed to Peter for safe-keeping, but the emperor Caligula wants it back to benefit from its powers. Marcellus former slave Demetrius seeks to prevent this, and catches the eye of Messalina, wife to Caligula s uncle Claudius. Messalina tempts Demetrius, he winds up fighting in the arena, and wavers in his faith.