...by Mary Torjussen, who is also an MNer.
I've just finished, after a couple of days where I've only put the kindle down at essential times (to keep the children alive and entertained, mainly). Wow! Brilliantly plotted, a twist I thought I had predicted but then in fact had not, utterly compulsive reading. Highly recommended.
Thanks Mary! When is the next one...and are your older novels available anywhere?