This is the most brilliant writing trick I've ever seen a genre author pull. 
 I was prepared for the traditional plot of "Family gets disturbed girl exorcism." The narrative lens was good and the addition of a reality show element was great, so I was hooked. 
 Tremblay sets up the ambiguity of "Is she really possessed?" early on. Normally I can feel a little let down during a horror novel if it turns out to be all a trick, but this time I decided halfway in that I didn't care. The personalities of and conflicts between the family members was so fleshed out that I knew that would love the book whether it went full Exorcist or full Scooby-Doo. It's written that well, and absolutely deserving of the awards it got. 
 Then I was knocked on my ass by that ending. Tremblay plays a mean game here, and I have to applaud him. 
 Spoiler ahead. 
 I mean a big-ass spoiler. 
 Look, I'm giving away the trick. I'm about to do the literary equivalent of spoiling The Prestige. If you haven't read the book, read it and come back. You deserve to experience it like I did. 
 I mean, I caught the tip of the reference. I recognized the significance of the name. Yet I was still unprepared. Even as it spiraled out of control, I disbelieved at how far Tremblay would take it. 
 (view spoiler)[You start out thinking that the book is a deconstruction of the exorcist genre. It does that for about two-hundred and fifty pages. Then, with barely twenty pages to go, you realize Tremblay has named our protagonist and staged the whole thing just to reenact Shirley Jackson's We Have Always Lived in the Castle. 
 He even namedrops The Haunting of Hill House! By the time Merry becomes the spiritual descendant of We Have Always Lived in The Castle's Merricat by recreating her poisoning scene, I was stunned that I didn't see it coming and amazed that I didn't feel cheated. 
 (hide spoiler)] 
 You tell me a story that good, you deserve to pull that off. 
 I went to play, realized the entire play was to set up a single magic trick, and loved both the play and the trick. Bravo.