Finding herself the victim of a violent monster attack, Jane launches a vigilante campaign to hunt the beast that tried to kill her. Jane's efforts intensify, but her troubling history of drug use and mental illness bubbles to the surface causing her family, community, and authorities to question the authenticity of her account. Suddenly alone in her fight, Jane starts to doubt her own memory of the attack...to doubt if Monster exists at all.

一群大学好友拿到了人气音乐节的入场券，他们带上了自己所需的一切准备在音乐节上狂欢。可是世事难料他们因一场交通事故无缘音乐节，只能被迫暂时在一家民宿中过夜。打算在民宿中狂欢一夜的他们却因为一位不速之客的加入陷入了疯狂的噩梦之中。