Just as you try to classify it, Laurent Binet ducks and sends you off on a tangential line of thought you couldn't have dreamed up. Historical, action novel? No, too deconstructed for that. The psychology of the architect of the Holocaust? No, it's about his killers. Identifying with the soul of Prague? Well, if we could ever learn the lessons of history .... Don't try, just let yourself be captivated.
Hitler knows that Heydrich is a rising star ready to do anything to further his own ambitions. This doesn't shock him, though, and for good reason. Couldn't the same thing have been said about Hitler himself? Hitler respects Heydrich because he combines fierceness with efficiency. If you add to this his loyalty towards the Fuehrer, you get the three elements that make the perfect Nazi. And that's without even mentioning his pure Aryan appearance.