The incident that first brought Gamache and Beauvoir together, that awful case, rushes back into Gamache's and Beauvoir's minds. Did the death of their mother leave them permanently damaged? Have those horrible wounds, which have been covered up for years, become worse and are poised to erupt? A letter written by a long-dead stone mason is uncovered when Chief Inspector Gamache investigates, raising him concern. The author relates his horror as he bricks up a room in an attic someplace in the village. The letter, which is 150 years old, is dreadful in every word. The villagers choose to enter the room after discovering it. As the bricks are removed, Gamache, Beauvoir and the villagers discover a world of curiosities. But the head of homicide soon realizes there's more in that room than meets the eye. There are puzzles within puzzles, and hidden messages warning of mayhem and revenge.