Erin is one of six teenagers who decide to take a summer trip together to a local campground. Prior to their arrival, a deranged man named Mike Corman kills several other young adults in a brutal fashion. It is said that years ago Corman was a serial killer who tortured and murdered four girls before being burned in a fire. He continues his slaughter until only Erin, her boyfriend Danny and another girl, Julie, are left.
Corman manages to wound Danny, while Julie - in a surprising twist - sucker-punches Erin, and then ties her up. Julie reveals that she is Mike's sister, and that it was Erin who started the fire that maimed and disfigured her brother. The vengeful sibling intends for Mike to get a little deadly payback, but Erin manages to escape. Julie chases her down and attempts to drown her in the lake, but is killed when Erin bashes her skull in with a pipe.
Mike pursues Erin, but is ultimately decapitated by her. The following morning, Erin visits her wounded boyfriend inside of the back of an ambulance, and reveals a secret to him: She was the one who originally murdered the four girls all those years ago, and helped to frame Mike for it. Erin then murders Danny via suffocation, and then waltzes out of the ambulance; flashing one last smile towards the camera before the film ends.