The film begins with a teenage girl, Laurel Miller (Jessica Lowndes), going into the woods to meet her boyfriend Michael (Randy Wayne). He gives her an early birthday present, but her father (Jamie McShane) shows up and demands that she leave with him. As they drive home, Laurel tells him that she will be marrying Michael as soon as she turns eighteen. He breaks down and apologizes to her, telling her he can't let her turn 18, then purposely crashes their car. Seeing that she is not dead, he kills her with a broken piece of mirror, saying he couldn't let the darkness take her.
After causing a botched exorcism that resulted in the death of a fellow priest and a pregnant woman, Father John Barrow (Devon Sawa) is committed to a Catholic mental asylum. Chaplain Henry Davies (Peter MacNeill) informs him that the Vatican has revoked his status as a priest. Meanwhile, Molly Hartley (Sarah Lind), the morning after celebrating both her twenty-fourth birthday and becoming the youngest partner in her firm, is arrested after police inspecting her home after a noise complaint finds the corpses of the two friends she engaged in a threesome with the night before. While interrogating Molly, she hears strange noises before she begins to have a deeper voice and refers to herself as "we". She is sent to the same mental asylum for psychiatric evaluation under Dr. Laurie Hawthorn (Gina Holden), but her condition worsens after an insect-like creature enters her body.