Horror for sure. There was a tension almost constantly. The second half was a wild ride. Memorable for sure, but also not something I am running out to tell all horror fans to read. ... Editing this a few days later. Bumped review from 3.5 to 4. In hindsight it is a very memorable book and I think if I had been in a more quiet place when I was reading it, it may have scared the crap out of me.