White Crow by Marcus Sedgwick
Sixteen-year-old Rebecca moves from London to a small, desolate village crumbling into the sea, when her policeman father is involved in a scandal at his job.  She becomes friends with Ferelith, a Goth girl who likes "things that are frightening." They spend the summer together exploring the village's sinister history. Back in 1798, the town's local priest was involved in a devilish experiment, one that suddenly also involves the two girls. Warning: you will have to finish this book, if you want to be able to sleep without nighmares!
Audience: Teen