After a single mother (Carice van Houten) witnesses terrifying symptoms of demonic possession in her 11-year-old son (David Mazouz), a Vatican representative (Catalina Sandino Moreno) calls on wheelchair-bound scientist Dr. Seth Ember (Aaron Eckhart) to rid him of the evil spirit. Driven by a personal agenda rooted in his own tragic past, Ember enters the boy's unconscious mind where he confronts a demon as ferocious as it is ingenious.