Edinburgh's most famed detective duo must face their most metaphysical mystery yet. A mysterious woman has pleaded for the help of Frey and McGray. Her son, illegitimate scion of the Koloman family, has received an anonymous death threat - right after learning he is to inherit the best part of a vast wine-producing estate. She offers miraculous waters from a small island in remote Loch Maree to heal McGray's sister. Murder and increasingly bizarre happenings intermingle in this trip to the Highlands.