No Good Deed by Manda Scott

Orla McLeod knows too much about violence for her own good. She knows about pain and how to inflict it, she knows about guilt and she knows about survival. And because she was barely a teenager when she learnt all this, she know what these things can do to a child. So when she and a nine-year-old boy are the only ones left alive in a freezing Glasgow tenement after a Special Branch undercover operation she was spearheading has gone disastrously wrong, there's no way Orla McLeod's going to hand Jamie Buchanan over to social services. Not when Jamie's the sole witness to Tord Svensen committing an act of savagery of the type that's rapidly turning him into one of the most feared criminals in Europe. Especially since Svensen knows a lot about survival too.