The Fox in the Attic by Richard Hughes.
 
Augusten is a young man from an aristocratic family, struggling to make sense of a world devastated by the Great War. The enemy abroad may have been defeated, but when he finds himself implicated in the death of a young girl, he becomes targeted as the enemy within. Fleeing Britain, Augusten seeks refuge and solace in the remote castle of Bavarian relatives; but what he finds is a hinterland of fierce lust and terrible darkness; a paradigm of the hunger and the hatred that promises to resuscitate a ruined Germany.
 
The Fox in the Attic is the first part of the unfinished novel The Human Predicament.