Tabula rasa - Ruth Downie

The medicus Ruso and his wife, Tilla, are back in the borderlands of Britannia, where he is tending the builders of Hadrian's Great Wall. Having been forced to move off their land, the Britons are distinctly on edge and are still smarting from the failure of a recent rebellion that claimed many lives.
The tension grows when Ruso's recently arrived clerk goes missing and things go from bad to worse when the young son of a local family also vanishes. While struggling to keep the peace between the Britons and the Romans, Ruso and Tilla uncover an intricate deception involving slavery and fur trappers, and it becomes imperative that they solve the mystery of the two disappearances before it's too late.