But the real achievement here is the lavishly, often hilariously detailed portrayal of the world that absorbs Ruso’s exhausted wits and energies (Downie even manages a few good jokes about English cuisine). The mystery is a good one, enriched with enigmatic images and episodes (an “invisible dog” hounding the compound, a suspicious case of food poisoning), and a secondary enigma buried in the identity and nature of the goddess whom Tilla stoically worships. The unusual suspects include bar owner (and probable procurer) Merula, sinister entrepreneur Claudius Innocens (identified, in the amusingly annotated list of “Characters” that precedes the narrative, as “a sleazebag”) and Ruso’s Uriah Heep–like nemesis, nitpicking hospital administrator Priscus. Ruso “buys” the uncommunicative Tilla and installs her as his house servant and cook, eventually gleaning from her information that suggests somebody is kidnapping freeborn girls and selling them as slaves. But these problems are trivial compared with the nightmare that builds from the discovery of a murdered slave girl’s body, then the rescue of a girl named Tilla with a broken arm evidently caused by a savage beating, then another female slave’s dead body. He’s recently divorced, overworked, at constant odds with military authorities and further burdened by demands made by his civilian brother on behalf of their financially strapped family. The title character, Gaius Petreius Ruso, is an army physician attached to a legion based in Deva (later Chester). (Mar.Dark doings in Roman-occupied “Britannia” are investigated in this nifty historical mystery, the award-winning English author’s first novel. Downie's auspicious debut sparkles with beguiling characters and a vividly imagined evocation of a hazy frontier. Tilla plots her escape as she recovers from her injuries, and just when Ruso becomes attached to her, she runs away, complicating his personal life and his investigation. Gaius becomes a reluctant detective, but his sleuthing threatens to get him killed and leaves him scant time to work on the first-aid guide he's writing to help salvage his finances. Meanwhile, young women from the local bordello keep turning up dead, and nobody is interested in investigating. Gaius rescues and buys an injured slave girl, Tilla, from her abusive master, but she refuses to talk, can't cook and costs more to keep than he can afford.

His quarters are filthy and vermin-filled, and his superior at the hospital is a petty tyrant.

Gaius Petrius Ruso, a military medicus (or doctor), transfers to the 20th Legion in the remote Britannia port of Deva (now Chester) to start over after a ruinous divorce and his father's death. The salacious underside of Roman-occupied Britain comes to life in Britisher Downie's debut.

Medicus by Ruth Downie