The first, and best, is In the Woods, by Tana French. Set in Ireland, it's an engrossing detective story with a good narrator and lots of interesting sub-plots. There's a sequel to it, The Likeness, which I haven't read, but very much intend to.

The next book is a true crime novel, The Monster of Florence, about a serial killer in Florence during the 70s and 80s. It's interesting and scary at the beginning. It is less good as it begins to focus on the absurd police response. That part is definitely interesting, but not as good as the first part.