Leonidas, champion gladiator of Rome, is set free from the games by a mysterious benefactor who grants him freedom, a place to live, and a servant—Cassia, a scribe—to look after him.

But the benefactor is only so generous—Leonidas must pay his own way and Cassia's, which means hiring himself out. The sharp-witted Cassia quickly lands him a post as a bodyguard, escorting a retired senator to Ostia.

The journey soon turns deadly, as Leonidas and Cassia find themselves squarely in the middle of intrigue that reaches from the slums of the Subura to the Palatine Hill and the emperor Nero himself.