Actually I was sure I had reviewed the book but it appears I didn’t.
Well, the short version is that this is the Twelfth book in the Bernie Gunther series. This one has the post-War Gunther on the run from the East Germans which causes him to reflect on an investigation that took him to Hitler’s Alpine retreat just before the war.
Prussian Blue is just as good as the others in the series and I can’t recommend it highly enough. It’s out today in paperback.