The empire is settled from its civil wars with a new, strong ruler in Septimius Severus, and while the emperor campaigns in the east, a cohort of Praetorians has been left in control of Rome under Rufinus, now a tribune of the Guard.

But adventure calls once more, as Rufinus receives a worrying letter that sends him on a quest in the north, which will take him and his new faithful companion to the edge of empire, where he will uncover a secret that puts the whole world in danger.