3.5 stars.
I really enjoyed this story overall. I found it genuinely creepy in a number of sections, and it utilised its environment really well (i.e. a lot of great creepy settings like dark apartment blocks and elevators). I was also very curious throughout the entirety of this story, and had so many questions about what was going on - overall, I think that the author did a good job at answering these, however I did have a few issues.
My only problems with the book were:
1) The issues I mentioned above - while I did think the novel had a good ending, I didn't like the parts that were resolved through non-supernatural means, only because they made absolutely no sense. It was a bit frustrating, especially when we were presented with things that couldn't be answered by with logical and realistic actions and situations.
2) I found the main character slightly annoying. Not unbearably so, but some of her behaviour in this genuinely had me frustrated.
3) The ending was a little bit too chaotic, with a lot of things happening really quickly. I've noticed that this is something that has happened in all of the Amy Cross book's that I've read so far, and I'm not really a fan of this style of writing. It comes off as a bit comedic at times, which didn't really fit with the overall tone of the story.
Overall, I did enjoy this novel, and would definitely recommend it.