Tabula Rasa (Gaius Petreius Ruso Series #6)

The medicus Ruso and his wife Tilla are back in the borderlands of Britannia, this time helping to tend 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.

Then Ruso's recently arrived clerk, Candidus, goes missing. A native boy thinks he sees a body being hidden inside the wall's half-finished stonework, and a worrying rumor begins to spread...