Death Behind Every Door by Heather Graham

In the shadows of a Scottish castle, something deadly is lurking in every corner…

When FBI special agent Luke Kendrick discovers chilling evidence of dozens of victims at a crime scene in London, he recognizes the calling card of the notorious H. H. Holmes Society. Named for the nineteenth-century monster regarded as America’s first serial killer, the society is comprised of a twisted web of killers, working to carry out heinous murders in Holmes’s memory. And now the group’s been linked to a Scottish castle turned B and B—where guests check in but never check out.
Arriving at the sinister Graystone Castle posed as a tourist, Luke is joined by Special Agent Carly MacDonald, and the pair is immediately confronted by dangers hidden in the castle’s depths. With guests disappearing and a network of killers closing in, Luke and Carly have only each other to rely on—and they’ll have to race to cut off the head of the snake before the blood trail of the past can culminate in a very real and deadly present.