The year is 1808. Davey Ten, a promising Gunwharf Rat, has finished a year of medical school at the renowned University of Edinburgh. It's been a tough year for Davey. Students and faculty alike have been informed of Davey's early workhouse years, his questionable parentage, and his lowly status. These bigots have condemned him by silence, which is killing his spirit. All Davey wants is to return to St. Brendan's.

Master Able Six finds a solution. Why not send along another Gunwharf Rat to keep him company? Able's grandmama, a Scot of wealth and influence, arranges for the two Rats to stay at her Edinburgh house, maintained by Esther Teague, a spinster.

Fellow Rat Avon March returns to Edinburgh with Davey. Adept at skulking, Avon will provide needed conversation, but also try to learn about the mysterious disappearance of a Royal Marine sergeant and Royal Navy warranted officer, from the hospital's famed Royal Infirmary.