A group of soldiers are picked by the chief of the Frumentarii, the Roman empire’s shadowy spy service, for an impossible mission. They must cross into Persian territory and rescue Prince Sasan, who is held at the formidable Castle of Silence. The ten set out, a motley crew of Romans and easterners. When their leader is killed, the second-in-command, the young boozy wastrel Valens, must take command. But one of his crew is a traitor and his men begin to meet grisly ends. They journey across the Euphrates and into Mesopotamia, the wild borderland between the Persian and Roman empires. Sidebottom conjures up this landscape and its people brilliantly. We meet religious fanatics and Arab brigands, Persian eunuchs and nomadic Heruli tribesmen, who bind their children’s heads to create long, pointy skulls. I could have journeyed with Valens and his crew for another 1,000 pages.