*slight spoilers, but nothing that you can't find on the inner cover or that ruin the story. However you are warned* 
 When I saw that the author or Horrostor had a new novel I had to grab it, Horrostor had been interesting, not just in content but execution. My Best Friend's Exorcism did not disappoint. The novel is contained within a fake year book during the 80's. 
 From page one the story grabbed me, Abby is an interesting character, she attends a private prep school on scholarship and becomes friends with Gretchen who is from a rich family who doesn't allow her to watch tv or movies and are religious and republican. 
 We see the girls age into Sophomores in High School going through normal teenage issues, like being popular, boys, drinking, smoking, drugs, acting out, trying to get good grades and mainly being friends and enjoying their time together. 
 Until the girls take LSD and Gretchen gets lost in the woods and things change. At first I thought this novel might be funny, or "demon" was a buzzword used and would wind up meaning Gretchen had a major mental disorder, but no, to my (happy) surprise this novel is actually about a girl who gets possessed by a demon. And not the split-pea-soup-fucking-herself-with-a-cross-speaking-in-tongues type. But a demon who tries to act like Gretchen and makes Abby's life miserable and hurts a lot of people involved, without too much...ummm...demon magic? 
 There are several parts I cringed at while reading; as Gretchen get's Abby kicked out of school and blamed for everything from having "inappropriate" relations with Gretchen to stealing a dead baby cadaver. I enjoy it when a novel brings out genuine uncomfortableness. 
 Abby was a great character, very real and very well written. In fact aside from Abby's parents I enjoyed how the author made all the characters have decent backgrounds and depth; their own personalities. 
 Some scenes in this book are quite disgusting so trigger warnings for : self harm, vomiting and bugs. 
 The actual exorcism is a really good scene and takes a very interesting turn and a great twist to the boring stereotype of an old priest with a collar speaking in Latin. 
 The reason this is getting four stars instead of five is for two reasons: 
 1) This novel fell into an area too many books are going now-a-days. Comic book level villainy from parents. Parents who don't care about their kids, are totally non-loving shitty asshats. I get it makes good drama, but it's becoming an all too often used trope. 
 2) Abby is almost too coincidentally a scapegoat for EVERYTHING bad that happens. Evil Gretchen has too easy of a time convincing everyone; teachers, her friends, school officials, the whole town, that the quiet, extremely smart, hard working and friendly Abby is actually a drug pushing deviant out to cause trouble. 
 I enjoyed this book, it made me remember my child hood and miss certain friends I am not in touch with anymore. It also gave me some very disturbing mental images to sleep with tonight.