A murder mystery set in a Roman port in second century Britain. Intended as the first of a series, there are two main characters, although one - the legion doctor implied in the title - seems to be the main detective.
In this story, he inadvertently gets involved in the mystery due to his bad luck to be on duty when the corpse is brought to the army hospital. He then ends up buying a native slave (who, it turns out, ends up being his crime-solving partner).
Both the doctor, Ruso, and the slave Tilla are interesting characters. Ruso is appealingly cynical about most things. The author also seems to be trying to get revenge on petty bureaucracy with her description of the way the tyrannical hospital administrator runs the place (to Ruso's great disadvantage).
Well worth a read.