We Have Always Lived in the Castle by Shirley Jackson
I read Shirley Jackson's short story "The Lottery" in middle school, and it stuck with me. It was so dark and subtly terrifying, and I think what made it so awfully scary is that it was about seemingly normal people who are, in reality, completely insane. And honestly, I don't think there's anything scarier than that.
I think the opening and closing paragraphs of her most famous book, The Haunting of Hill House, are among the best ever written. It still gives me goosebumps:
"No live organism can continue for long to exist sanely under conditions of absolute reality; even larks and katydids are supposed, by some, to dream. Hill House, not sane, stood by itself against its hills, holding darkness within; it had stood for eighty years and might stand for eighty more. Within, walls continued upright, bricks met neatly, floors were firm, and doors were sensibly shut; silence lay steadily against the wood and stone of Hill House, and whatever walked there, walked alone."
I had never heard of We Have Always Lived in the Castle, but I saw it mentioned in a list titled something like "The Best Creepy Books Ever" (I'm a sucker for lists like that), and decided to try it out.
There are no ghosts in this book. There is no supernatural activity of any kind. No one gets an axe and decides to get chop-happy with anyone's head. In fact, it reminds me of a much darker version of The Glass Menagerie.
But this book gave me the severe heebie jeebies.
It all centers around the Blackwood family, and in particular, an 18-year-old girl named Mary Katherine. She lives in a house with her older sister, Constance, and their ailing Uncle Julian. She tells the readers in the first chapter that the rest of her family is dead. She's the only one who will leave the house, and only when it is absolutely necessary to do so. She hates everyone in the town, and they return the sentiment.
Jackson does such a great job of slowly amping up the shiver factor - letting you see what's really going on with the Blackwoods, and why they are the way they are. The ending is unbelievably unsettling and wholly devastating, and I've been thinking about it ever since.