Scunnered is a Scottishism I've picked up from dh; it's sort of like when you eat so much of something you love that it makes you sick and you can't stand the sight of it again. I think. I actually read quite a bit of detective fiction and I think JD is pretty great. One thing I liked about this that set it apart from typical whodunnits is that you know whodunnit from the start, and the story is all about the chase.
Another thing, do you remember towards the end when Kathryn's mum hears something outside while Pell is on the run, but it turns out to be nothing? I wondered if he'd maybe tried out a different ending and that was a little bit relating to it that got left in.