Gaius Valerius Verrens returns to Rome from the successful campaign against Boudicca in Britain. Now hailed a 'Hero of Rome', Valerius is not the man he once was – scarred both physically and emotionally by the battles he has fought, his sister is mortally ill, his father in self-imposed exile. And neither is Rome the same city as the one he left.

The Emperor Nero grows increasingly paranoid. Those who seek power for themselves whisper darkly in the emperor's ears. They speak of a new threat, one found within the walls of Rome itself. A new religious sect, the followers of Christus, deny Nero's divinity and are rumoured to be spreading sedition.

Nero calls on his 'Hero of Rome' to become a 'Defender of Rome', to seek out this rebel sect, to capture their leader, a man known as Petrus. Failure would be to forfeit his life, and the lives of twenty thousands Judaeans living in Rome. But as Valerius begins his search, a quest which will take him to the edge of the empire, he will discover that success may cost him nearly as much as failure.