55 AD. Trouble is brewing on the eastern borders of the Roman Empire, once again the tribune Cato and the centurion Macro need to prepare for war... The treacherous Parthian kingdom has invaded Armenia, a border state that Rome claims as part of its ambitions, expelling King Radamist. Although the king is ambitious and ruthless, he is vital to the strategic interests of Rome. The commander Corbulo must return him to the Armenian throne, as well as prepare the army for war with the powerful Parthian kingdom. Corbulo orders the newly arrived Cato and Macro and their elite cohort of Praetorian Guard to carry out this task. They must march through uncharted and unfamiliar terrain to restore an unpopular king to the throne - a dangerous mission. Allies cannot be trusted, and enemies lurk on all sides. The bravery and skill of the Roman army will be tested to the limit...