In this book Harry Hole (Nesbo's main character) earns himself an unearned promotion, and is transferred out of the Crime Squad and onto the squad that investigates Neo-Nazi, Communists, and, one imagines, Green groups.
While there, he stumbles on a plot that suggests someone in the Government is going to be assassinated, so he sets off to investigate the likely suspects, which includes Norwegians who signed up to fight in Hitler's army because of their loathing of Stalin.
Sure enough, he solves the problem, even if it gets a little convoluted on the way (at one stage we get a discussion of Multiple Personality Disorder as a reason reason for murder towards the end of the book).
On its' face it sounds silly (WWII Nazis possibly involved in a millennial attempt on someone's life), but I suspect people will enjoy it all the same, because it's told so well.
Incidentally, try it read the books in order, as Hole solves a crime in a later book that starts here.