In 229CE, Hadrian's Wall in Britannia, and the brave auxiliary soldiers who man it, provide the physical security for the northern frontier of the mighty Roman Empire. However, only an enlightened few understand the graver supernatural threats lurking amid the dark forests and trackless marshes of the border region - and in the hearts of men. Those enlightened few are yourselves, the Brotherhood of Mithras, who serve among the auxiliaries. Last night sentries from your fort killed a man trying to sneak over the Wall from the north - but not before he had improbably thrown one from the wall-walk to their death. The cohort Prefect is furious and, since there were further unusual aspects to the man, has ordered you to investigate. The man shouted incomprehensible words and had strange wounds on his hands - perhaps this incident is connected to recent reports of similar afflictions?

The staff of Smythe's Discreet Investigations, London's first — indeed, only — all-female detective agency, are busier than ever as everyone's help is needed to handle an important and sensitive — and unusual — case, with potential ramifications reaching into the corridors of power, and perhaps beyond. Edwina Sandringham-Smythe, the agency's owner, has hired a new assistant, but not everything is going to plan. Is the assistant who she says she is and, if not, what are her motives for coming to the Agency; who, or what, is she really working for?