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 eighteenth-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.

Four bodies have been discovered along Europe’s riverbanks, placed with care—and completely drained of blood. Pinpricks on their throats indicate a slender murder weapon, but DNA found in the wounds suggests something far more sinister. Tasked with investigating, the FBI recruits Agents Della Hamilton and Mason Carter to Blackbird, an international offshoot of the Krewe of Hunters. If you want to catch a vampire killer, you need agents who can speak with the dead.

Deep in the Florida Everglades, the body of a woman is discovered in pieces, presumably ravaged by an alligator. Upon closer inspection, it’s determined no animal could make such perfectly precise cuts. Only a blade could do that. Wielded by a human. Soon, dozens of oil drums emerge amid the river of grass. Each one packed to the brim with body parts.

When two hikers go missing within a series of daunting caves outside of Denver, Colorado, FDLE special agent Amy Larson and her partner, FBI special agent Hunter Forrest, have good reason to suspect foul play. The pair of hikers are only the latest to vanish after a rash of disappearances that’s left local law enforcement stumped. But in searching the dank caverns near the Arkansas River, the agents aren’t prepared for the horror they uncover: a muddy pit littered with corpses. Covered in bite marks. Made by human teeth.

A ritualistic murder on the side of a remote road brings in the Florida state police. Special Agent Amy Larson has never seen worse, and there are indications that this killing could be just the beginning. The crime draws the attention of the FBI in the form of Special Agent Hunter Forrest, a man with insider knowledge of how violent cults operate, and a man who might never be able to escape his own past.