I almost literally couldn't put this down. Walton's setting is an alternate 1948, where Britain made peace with Germany in 1941 after Rudolf Hess's mission; and her viewpoint characters are a young aristocratic woman married to a Jew, and a homosexual Scotland Yard detective investigating a murder, as Britain slides into totalitarianism. It is a story of the seamy underside of respectability and conformity, and of the discovery of unlooked-for courage. It is a crime novel that turns into a political parable. Brilliant stuff, with some lovely nods to our timeline especially in the last few chapters, and riveting characterisation.
(My only complaint is that Walton is not on totally firm ground with her nobility - baronets do not sit in the House of Lords, and there seems confusion as to whether one character is the Duke or the Earl of Hampshire.)