Lapped by the gentle waters of Locust Lake, the small resort town of Tranquility, Maine, seems like the perfect spot for Dr. Claire Elliot to shelter her adolescent son, Noah, from the distractions of the big city and the lingering memory of his father's death. But with the first snap of winter comes shocking news that puts her practice on the line: a teenage boy under her care has committed an appalling act of violence. And as Claire and all of Tranquility soon discover, it is just the start of a chain of lethal outbursts among the town's teenagers.