The Massachusetts museum Scarlet House shows signs of being haunted, so Gemma Doyle, owner of the Sherlock Holmes Bookshop and Emporium, tries to get to the bottom of it. Gemma doesn't believe in ghosts, but in this ninth outing (following A Three Book Problem), Gemma and Jayne stumble across a dead body, and must consider an all too physical threat. Despite Gemma's determination not to get further involved, it would appear that once again, and much to the displeasure of Detective Ryan Ashburton, the game is afoot.