A Head Full Of Ghosts by Paul Tremblay.
This is one chilling book. Tremblay structures the book in such a way that you are led to believe the expected climax of the book is one that will haunt you but what does haunt and linger with you after reading the last page is something else entirely.
Fifteen years after her older sister Marjorie Barrett was believed to be possessed, twenty-three year old Meredith – Merry – Barrett recounts those events to a writer chronicling those events. Most of the events are recalled from a then eight year old Merry’s perspective making her the unreliable narrator of the story. With her religious father out of work and her mother unable to earn enough to prevent the loss of their home, Marjorie’s medical bills force the Barrett’s to make a tough decision. They reluctantly accept a lucrative offer to have a TV crew come in and air a reality show chronicling Marjorie’s fall into madness and eventual exorcism.
This is one lean and mean scary book.