Mia (Jane Levy), a drug addict, is determined to kick the habit. To that end, she asks her brother, David (Shiloh Fernandez), his girlfriend, Natalie (Elizabeth Blackmore) and their friends Olivia (Jessica Lucas) and Eric (Lou Taylor Pucci) to accompany her to their family's remote forest cabin to help her through withdrawal. Eric finds a mysterious Book of the Dead at the cabin and reads aloud from it, awakening an ancient demon. All hell breaks loose when the malevolent entity possesses Mia.