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.

As the rash of disturbing behavior grows, Claire uncovers a horrifying secret: this is not the first time it has happened. Twice a century, the children of Tranquility lash out with deadly violence. Claire suspects that there is a biological cause for the epidemic, and she fears that the placid Locust Lake may conceal an insidious danger. As she races to save Tranquility—and her son—from harm, Claire discovers an even greater threat: a shocking conspiracy to manipulate nature and cause innocents to slaughter.