The book: Dark Places by Gillian Flynn
The hook: The sole survivor of her family's mass murder in their home, a little girl is now a fully grown train wreck who begins to doubt her young testimony that her brother was the killer. The narrative jumps back and forth in time, taking us through the day of the tragedy from the perspective of all the characters involved.
Fear factor: Life (or death) sucks for pretty much all the characters in this story, so it can be just as depressingly sad as it is terrifying.