Centurion Aurelius Castus - once a soldier in the elite legions of the Danube - believes his glory days are over, as he finds himself in the cold, grey wastes of northern Britain, battling to protect an empire in decline. Here he must face the barbarians beyond Hadrian's Wall, in a mission riven with bloodshed and treachery. Can Castus keep his promise to a woman he has sworn to help? And is anything about this doomed enterprise what it seems?