Nesbo is a crime writer of renown, no need to introduce him and his 10 or so crime novels. A few years ago I started reading crime novels as a break from 'real' reading. Even though I read them quickly and don't expect a lot from them, I try and find authors who can actually write well and tell a story.
I find Nesbo to be inventive and spinner of a good yarn. This one took about a third of the book to really get into the story but then it was easy to get hooked. This one and The Snowman are my two pick of his novels.
Set in Oslo, with Harry Hole as flawed main detective, we have two stories threaded through the book. One is set in WW2 where Norwegian soldiers defect and fight for the Germans. And in modern day a security assignment goes horribly wrong and implicates Hole.
A very specific kind of sniper amo is found in a forest and the rifle traced to an old man...There is a Neo-Nazi element in Oslo underworld who seem to be involved as well. The novel is written as a clever puzzle and kept my attention to the end.
The Snowman is another Nesbo worth reading. It involves, among other things, a snowman. You will never innocently look at a snowman again.