Once a soldier in an elite legion from the Danube, Aurelius Castus believes his glory days are over, stuck in Britain's provincial backwater. But history is about to take a hand and when the king of the Picts, the savage people beyond Hadrian's Wall, dies in mysterious circumstances, Castus is selected to command the bodyguard of a Roman envoy sent to negotiate with the barbarians. But the diplomatic mission ends in bloody tragedy...