Son of a critical senator, tribune Marcellus Gallio offends imperial prince Caligula over a prestigious slave auction and is punitively posted to the garrison in godforsaken Palestine, as deputy of governor Pontius Pilate. Along comes his proud, indulgence-spoiled slave Demetrius. Clueless about the Messianic Jewish monotheism, they attend the crucifixion of 'Jesus king of the Jews'. The red robe which Marcellus wins playing dice with his detachment officers however seems to have magical properties: it terrifies the brazen tribune as never before by inducing nightmarish visions, but is estranged by runaway Demetrius. This poisons his life even after being allowed back to Rome, where his youth love Diana luckily has the ear of the superstitious old emperor, who still refuses a marriage, but is puzzled by the magic and allows Marcellus to return to Palestine of a quest for it. looking for Demetrius, Marcellus learns compassion and about charitable commoners before retrieving it. Returning home with Demetrius, he faces the hostile mad new emperor, Caligula, who craves Diana and persecutes the Christian sect, which she and both men have joined, a recipe for a bloody finale.