This is one of the better crime novels I've read, and the reason for that is that the author has stepped off the beaten track to produce something a little darker, grittier and less black-and-white than normal.
The storyline is relatively simple - a cop in Glasgow is working undercover in a drugs and prostitution racket to try to ensnare the brutal ringleader when her cover is busted. She avoids execution with the help of an emotionally stunted nine year old boy whose addict/prostitute mother has overdosed and subsequently flees to the highlands with him. A game of cat-and-mouse ensues alongside the emotional recovery of the woman and boy.
As another reviewer has said, this is not a comfortable moral tale and you will have to reconcile yourself to the questionnable morals and behaviours, but I think the complex motivations and emotional responses are part of the strength of the book. The author has in my opinion done a marvellous job with the characterisation of the leading two characters, with some other notable cast members in support. It is perhaps (and necessarily) only the villain who is underdone.
So a very respectable effort all round - well written, involving, engaging and with unexpected depth of character.