On the whole the story works quite well once you have read the whole book. I spent a considerable portion of the book thinking that Megan,Rachel and Anna were all the same person. There is no distinction in the way these people act and this remains consistent. The ‘voice’ of each of these is to all intents, identical. For a narrative which is entirely written from the first person perspective of all of these, it becomes possible for you to think that they all exist within the head of one person (potentially schizophrenic) and therefore when you finally realise that they were always intended to be different, the book is a let down.
I’m therefore moderately surprised that this got past any publishing editor. This disappointment is compounded by the revelation that, aside from the framing conceit of the set-up, it is a very average thriller.