55 A.D.. Problems are brewing on the eastern borders of the Roman Empire, again the tribune of Cato and the centurion Macron need to prepare for war... The treacherous Parthian kingdom invaded Armenia, a border state that Rome claims within its ambitions, expelling the king Radamist. Although the king is ambitious and ruthless, he is vital to Rome's strategic interests. Commander Corbulon must return him to the Armenian throne, as well as prepare the army for war with the powerful Parthian kingdom. Corbulon orders the newly arrived Cato and Macron and their elite Praetorian Guard cohorts to carry out this task. They have to march through unknown and unfamiliar terrain to restore the unpopular king on the throne - a dangerous mission. Allies cannot be trusted, and enemies lurk on all sides. The courage and skill of the Roman army will be tested to the limit.