I absolutely loved Witherstone; very well written, with good depth of characters. The heroine is very likeable and realistic, and the plot is really mysterious and believable - resulting in a huge amount of anticipation.
It's genuinely 'unputdownable', and was still circling through my mind long after I'd finished. Don't be put off by the slow-ish beginning - it only builds up suspense before the multiple climaxes later in the book, and gives the characters more detail.
I'd definitely recommend it to anyone - it's a fantastic book, and well worth the buy :)