Ancient Rome, during the time of Emperor Nero. Vinicius, a young patrician, falls in love with the beautiful Lygia, the daughter of a Barbarian commander who was killed in battle, and wants her for his concubine. For Lygia, a Christian, being a pagan's concubine is a severe sin and disgrace. However, when Vinicius is wounded, Lygia cares for him, and starts to reciprocate his feelings. Vinicius, in return, becomes interested in Christian learning and asks Apostle Peter to teach him. In the meantime, Emperor Nero accuses Christians of having started a great fire in Rome. He encourages the imprisonment, torture and murder of his Christian subjects.