FBI agent Francis York Morgan arrives in the rural Washington town of Greenvale to investigate the ritualistic murder of 18-year-old Anna Graham — found with red seeds near her body, matching a series of similar killings across the country. York's bizarre behavior and dismissive attitude toward locals generate immediate friction. He is assisted by the haunted sheriff George Woodman, deputy Emily Wyatt, and the meek assistant Thomas MacLaine. Throughout the investigation, York is attacked repeatedly by the Raincoat Killer — a figure who, according to local legend, only strikes when it rains — and has a habit of interrupting conversations to deliver private asides to an unseen person he refers to as Zach.