The Apolline Sibyl - a young adult thriller by Dave Becker

Jenna Hamilton attends an elite school for exceptionally gifted students. In the past year she has witnessed week-long darkness, hundred-pound hailstones, and plagues of blood and flies. Rumors of curses and the end of the world surround her small town of Clement, Massachusetts. As her sophomore year begins, an ancient giantess marked with a bizarre symbol arrives at her school, and satanic cult begins stalking her. It seems her terror has only just begun.