The book started off promising, but the last half was incredibly rushed.
One of the selling points of a good mystery is the build-up to the reveal of the culprit. Half of the fun for the reader is going through, looking for clues so that they can come to the conclusion of who the guilty party is on their own. (Or is it just me?)
This book didn't really have that.
It attempted it, sure. The book tried to draw some parallel between Bekki's recent break-up with her boyfriend, and situations not being quite what we expect them to be. But it fell flat. The parallel wasn't very well explained, and despite the real murderer having no reason to fess up to Becky, he tells her everything, with very little prompting.
What could have been an enjoyable mystery instead just became a rushed, confusing mess.