Edie and Heather couldn't be more different. Edie wears short skirts, is sassy, confident, popular and knows her own mind. Heather is overweight, shy, awkward and considered a loner.

But meeting at school in the sixth form, they become friends, until Connor becomes Edie's boyfriend.

Fast forward six years and Edie is living alone in a flat in London about to have a baby. She has no one she can call on for help, support or friendship yet when Heather visits her unexpectedly, she has a terrible sense of foreboding.

The reader doesn't know what happened to disrupt the relationship of the two girls, but little by little we find out more about their characters through the dual narratives.

Heather takes the 'Before' storyline, and Edie tells us what's happening 'After'.

What was this turning point?

It's not revealed until the very end of the book, and it doesn't disappoint - it's shocking and disturbing and plays on the reader's mind long after the book is finished.

This is a fascinating read which at first seems almost formulaic as it fits into the genre of bestselling psychological thrillers, the 'domestic noir' which is appealing to women particularly at the moment. But the clever ending makes this much more. Putting the book down, we actually want to revisit it, in order to reassess our reactions to the characters. Our sympathies, it seems, have been misplaced, haven't they? Who is the victim and the villain? It's a clever book, and a gripping read.