In northern Idaho, a summer camp aimed at helping a group of teenage girls bond with nature away from technology takes a dark turn. Promised a transformative experience, the girls find themselves in peril when their houseboat unexpectedly becomes stuck in the river. An unusual pair arrives, seemingly to assist them, but this gesture of goodwill quickly turns sinister. The girls are forced to flee into the forest, desperately trying to escape a relentless and vicious murderer. Meanwhile, every 40 seconds, another person vanishes.