The Mythmaker = Appointment in Vienna — Sarah Gainham

Kit Quest, a young English officer who, because he has a Hungarian mother and numerous Hungarian relatives, is sent on a secret mission to try and trace one Otto Berger, Hitler's personal and devoted servant, who had carried out many little private exterminations for his master and who had been in Hitler's Bunker up to the last. Kit looks up his cousin and her family and quickly involves himself in their troubles, only to discover to his horror that they know a good deal more about Berger than it is safe to know.