A demon possesses the body of an innocent 11-year-old boy and although his parents have called in the best exorcists, they've all failed. That's when the Vatican enlists the help of wheelchair-bound Dr. Seth Ember (Aaron Eckhart), an "Incarnate" who is able to enter the subconscious minds of the possessed and evict the demons from inside of their minds.

Once inside the boy's mind, the doctor is shocked to discover the same evil spirit who is responsible for the death of his own wife and child years before. As the demon inside the boy is the most powerful he's ever contacted, he's afraid that once he gets rid of the demon, the boy will die.