I'll start by saying that this book shouldn't have been in my school library (especially when its copyright page literally says it contains Bondage (sexual)). But did I read it anyway? Yes! (Probably not the most responsible idea . . . .)
Overall it was a good book, with an intriguing mystery and a cast of interesting characters. I had mo problem following Sarah through her highs and lows in the journey. 
There were some points in the book where the writing seemed amateurish—stilted dialogue, questionable formatting etc—but that didn't kick me out of the immersion too much. 
It also gave me more anxiety than thrills (y'know, because it's in the thriller genre), but I think that's the point, actually. 
It ended somewhat open-endedly, with a bit too much still hidden in the shadows for my liking. It felt like there wasn't enough explanation and closure. I'd've liked if there was another chapter or two to wrap it up, though the ending premise was good. 

I could smell a potential romance between Sarah and Jim (because of rhe set-up), but I'm glad it never happened and was just very basically established instead. I was worries it'd distract from the main plot and conflicts, phew. Sarah already has enough on her plate without having to deal with romance—especially considering her traumas.

In conclusion, I quite enjoyed reading this, and it opened my eyes to some aspects of psychology and criminal thinking. It also touches on trauma quite respectfully, which was nice. Would recommend to those looking for a dark psychological mystery.