The game is a footnote
(Book)

Sequel to: A three book problem.

Asked to look into some strange happenings at Scarlet House, a historical re-enactment museum, Gemma Doyle, owner of the Sherlock Holmes Bookshop and Emporium, and Jayne instead find a dead body and suspect foul play as secrets about the museum come to light.

Scarlet House, the oldest building in West London, Massachusetts, is now a historical re-enactment museum. 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. When Gemma and Jayne stumble across a dead body on the property, they're forced to consider an all too physical threat. With the museum being a revolving door for potential killers, they have plenty of options for who might be the actual culprit. -- adapted from jacket