Something Wicked This Way Comes by Ray Bradbury
Opening line: "First of all, it was October, a rare month for boys."
Brief synopsis: Two young boys become fascinated with a mysterious traveling carnival that comes to their Midwestern hometown one October. Lead by the sinister Mr. Dark, the carnival tests the boys' fears and has an odd effect on the locals.
What makes it scary: Bradbury is better-known for science-fiction novels like Fahrenheit 451, but Something Wicked This Way Comes is one of his best and most complete works, a deeply personal story about small towns, childhood friendships, aging, and the complicated relationships between fathers and sons.
Bradbury's lush prose gives the novel a dreamy quality, which easily transitions to the nightmarish. By orienting the story in the pubescent headspace of the boys, Bradbury preys on specific youthful fears -- like witches and skeletons, and disbelieving adults -- and skews the world that we know a few degrees past comprehension. That betrayal of reality is far scarier than any ghost or monster, and Something Wicked This Way Comes mines that sensation to great effect, specifically with Mr. Dark, whose mere existence feels illogical. Though the book is technically a coming-of-age story, the horror is almost more palpable for adults who can see the carnival as a metaphor for the trauma of growing up.