Not really for people who really are cat crazy, just saying

Child 44 - Tom Rob Smith

 

This is a good solid 3.5 for me.   For me, at times, the book relied too much on constantly shifting from the worst to best case scenarios.   It is so much the mystery that gets you, but the journal that Leo and Raisa go on in terms of themselves and their relationship.  The book also does make it feel like someone is watching you, so the atmosphere is done really well.