The date is 1882; the scene, New York City. There have been a series of murders of young women in Midtown, and the police are baffled. They believe the killer is surfacing from manholes in the sewer system, mutilating his victims, and returning back to the depths to escape. However, they are unsure whether the killer is of human or non-human origin. Dr. Bones takes up the challenge and is joined by a young woman whose wealthy family has decided to help the doctor with his new ambition. The investigation soon leads them to the Canarsee Indians and legends about sprites, known as Wemategunis (Wemas), that once inhabited the forests of Manhattan. By the late nineteenth century, the trees were mostly long gone, replaced by brick and mortar and the hustle-bustle of carriages, trollies and people hurrying to and from their destinations.

Who or what is responsible for the serial murders? Can the killing spree be stopped?

Bones and Missy work with a NYPD detective to try to solve the mystery and bring a halt to the gruesome events.