Marcus Vinicius is a Roman military commander and the legate of the XIV Gemina. Returning from wars in Britain and Gaul, he falls in love with Lygia, a devout Christian; in spite of this, he continually tries to win her affections. Though she grew up as the foster daughter of Aulus Plautius, a retired Roman general, Lygia is legally a Lygian hostage of Rome in the old general's care. Petronius, Marcus' uncle, persuades Nero to give her to his nephew as a reward for his services. Lygia resents this arrangement, but eventually falls in love with Marcus.