Scarlet House, now a historical re-enactment museum, is the oldest building in West London, Massachusetts. When things start moving around on their own, board members suggest that Gemma Doyle, owner of the Sherlock Holmes Bookshop and Emporium, might be able to get to the bottom of it. Gemma doesn't believe in ghosts, but she agrees to eliminate the impossible. But when Gemma and Jayne stumble across a dead body on the property, they're forced to consider an all too physical threat.
Gemma and Jayne suspect foul play as they start to uncover more secrets about the museum. With the museum being a revolving door for potential killers, they have plenty of options for who might be the actual culprit.
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.