Drunk and disillusioned Roman, Marcellus Gallio, wins Jesus' robe in a dice game after the crucifixion. Marcellus has never been a man of faith like his slave, Demetrius, but when Demetrius escapes with the robe, Marcellus experiences disturbing visions and feels guilty for his actions. Convinced that destroying the robe will cure him, Marcellus sets out to find Demetrius — and discovers his Christian faith along the way.

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.