In a remote mountain lodge, five sorority sisters accidentally unleash an unholy entity, and must battle evil and each other to stop it from devouring mankind.

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.