It is part Wodehousian (shut up - like you would know how to spell that) country estate comedy of manners, part Agatha Christie murder mystery, with a dollop of the old "what if Hitler won?" sauce. Obvious comparisons are to Phillip K. Dick's "Man in the High Castle", and Roth's "The Plot Against America". There's even a nod in the book to Roth's work with references to President Lindbergh. Walton's book, like those two, manages to be convincing in its depiction of a world gone slightly wrong; a "horseshoe nail" story, as it is put in the book, referring to the children's song where a kingdom was lost due to a chain of small events.
The plot is convoluted, like all murder mysteries should be. The characters are well drawn, believable, and earned my sympathy. They are given no easy ways out of a situation, and the conclusion is jam-packed with compromise and moral greyness. The British government's slide into 1984-style fascism is handled smoothly, setting up further novels in this milieu. Orwell's classic is name-checked amusingly in the book by one of the characters who thinks a bit of science fiction will cheer up her persecuted husband.
I just wrote the word "milieu", and what's worse I couldn't think of an alternative. What a ponce.
Like all of the Tor ebooks so far, this book has a sequel "Ha'penny" (= two farthings). This free book has done it's job well, and I'll be keeping an eye out for more work by Walton.