London PC Peter Grant gets called to the British Museum, which has a serious problem in one of its many basements. They think it's a poltergeist; something, at least, is moving things around in ways that can't be accounted for by the actions of staff and users. Grant thinks this is unlikely, because of how modern the building is, but given the ancient, rare, historical, and otherwise valuable items in the collection, can't rule it out.
And so he goes hunting through the basements. But is he hunting a ghost, a poltergeist, something else?
And has he brought the right equipment?
This is a nice little short story, an Audible exclusive, that adds to the world-building and character development of the series. It's an additional little treat if you've been reading the series, and a nice introduction to Peter Grant if you haven't been.
This story was free on Audible when I downloaded it.