Gil Cunningham had hoped that the first time he set foot in the brothel on the Drygate it would also be his last, but by the time all was settled he felt quite at home within its artfully painted chambers. The bawdy house, along with the neighboring property, is offered to Gil and his wife Alys by the forceful Dame Isabella. But matters are confused by an outbreak of counterfeit coins in Glasgow, which Gil has been ordered to investigate.
Then Dame Isabella is found dead in strange circumstances, and the more Gil pursues the cause of her death, the more false coins he finds. Rumors circulate that the Devil is abroad in Strathblane. By the time Gil and Alys have untangled matters, some very surprising-and sinister-things have come to light.