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. 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. When soldiers ransack the nearby farms looking for Candidus, Tilla's tentative friendship with a local family turns to anger and disappointment.

Ruso and Tilla, now newlyweds, have moved back to Britannia, where Ruso's old friend and colleague Valens has promised to help him find work. But it isn't the kind of work he'd had in mind - Ruso is tasked with hunting down a missing tax man named Julius Asper. Of course, there's also something else missing: money. And the council of the town of Verulamium is bickering over what's become of it. Compelled to delve deeper by a threat from his old sparring partner, Metellus, Ruso discovers that the good townsfolk may not be as loyal to Rome as they like to appear.

At long last, Gaius Petreius Ruso and his companion, Tilla, are headed home - to Gaul. Having received a note consisting only of the words "COME HOME!" Ruso has (reluctantly, of course) pulled up stakes and brought Tilla to meet his family. But the reception there is not what Ruso has hoped for: no one will admit to sending for him, and his brother Lucius is hoping he'll leave.

The edge of the Roman Empire is a volatile place; the tribes of the North dwell near its borders. These hinterlands are the homeland of Gaius Petreius Ruso's slave, Tilla, who has scores of her own to settle there: Her tribespeople, under the leadership of the mysterious Stag Man, are fomenting a rebellion, and her former lover is implicated in the murder of a soldier. Ruso, once again pulled into a murder investigation, is appalled to find that Tilla is still spending time with the prime suspect.

Ruso and Tilla's excitement at arriving in Rome with their new baby daughter is soon dulled by their discovery that the grand facades of polished marble mask an underworld of corrupt landlords and vermin-infested tenements. There are also far too many doctors - some skilled - but others positively dangerous.