This is Zombie Apocalyptic done really well, how the phenomenon came about and how it works set out more clearly and more credibly than in any other zombie story I've read. And the main characters, a man of 23, once a teacher, now trying to look after a mixed bag of children who survived, though far from unscathed, and a girl of 17 (I think) who has been on her own for a year following the death of her mother, are both very real and completely unforgettable.
Definitely not one to be missed if you like this sort of thing - and even if you don't. You may even change your mind about the whole genre!
And an "in-betweener"? Someone who has died then come back to life; not a zombie - yet.