He lurks in the abandoned subway tunnels under New York City. An Ex-Marine who was left to die in the jungles of Vietnam by his commanding officer back in 1975. Forty years later. Homicide Detective Iris Williams thought she'd seen it all until she and her partner Detective Annette Toni are called In to investigate the murder of an entire family. The case becomes a nightmare for the detectives as they crawl deeper and deeper into the mind of a man that the media is calling, THE PIGGYBACK KILLER.