Back at his post as a doctor in the Twentieth legion in Roman-occupied Britain, Ruso uncovers a new danger even closer to home than the neighboring barbarians.

As mysterious injuries, and even deaths, begin to appear in the medical ledgers, it's clear that all is not well amongst the native recruits to Britannia's imperial army. Is the much- decorated Centurion Geminus preying on his weaker soldiers? And could this be related to the appearance of Emperor Hadrian?

Bound by his sense of duty and ill-advised curiosity, Ruso begins to ask questions nobody wants to hear. Meanwhile his barbarian wife, Tilla, is finding out some of the answers-and marked as a security risk by the very officers Ruso is interrogating.

With Hadrian's visit looming large, the fates of the legion, Tilla, and Ruso himself hang in the balance.