Kerr has written a number of novels about a German police detective, Bernie Gunther, and this is the best so far, in my view. Gunther is the epitome of the hard-boiled Philip Marlowe-like PI. The context of the BG plots is Nazi Germany; Prussian blue takes place in 1939. Gunther is a socialist and anyone not a member of the Nazi party will always be viewed with suspicion by Gunther’s superiors. Then add in the characteristic that Gunther is a Berliner, which makes him flippant, disrespectful, subversive, sarcastic – the list goes on! But he is a good cop in difficult times, and his deductive skills force the Nazi superiors to use him in difficult and sensitive investigations. The novel dwells on the existential crisis of investigating a murder in the Nazi context. This is mystery writing at its best.