Parthia is vying with Rome for control of Palmyra, an officially neutral kingdom. Palmyra's royal household is on the brink of open revolt, and so a task force under the command of experienced soldiers, Macro and Cato, is dispatched to defend its king and guard its borders.

When Parthia hears of the Roman army's presence, it starts amassing its troops for war. Macro's cohort must march against the enemy, deep into treacherous territory. If Palmyra is not to fall into the clutches of Parthia, they will have to defeat superior numbers in a desperate siege.

The quest for a lasting peace has never been more challenging, nor more critical for the future of the empire.