Farthing is a country house murder mystery, set in an alternate time-line where Britain and Nazi Germany have made peace some time after the fall of Dunkirk. Germany and the Soviet Union are waging a protracted war, while an isolationist U.S. remains at peace with an imperialist Japan. England is presented as a rigidly class-bound society sliding towards Fascism.
Of all the characters in the book, David Kahn has the most faith in the Anglo-Saxon values of fair play, values whose fragility Walton is out to demonstrate. Kahn is a Jewish moneylender -- or micro-credit entrepreneur -- who has married into a posh English family.
Farthing illustrates how dependent the English mystery novel is on traditions of due process and rational inquiry. Carmichael seems like a standard-issue detective, gruff but fundamentally decent – until we discover that in England the rule of law has petered out. The effect of this discovery in the context of a mystery novel is genuinely shocking -- one of the key moments where the cozy catastrophe stops feeling so cozy...
Trilogies typically jump the shark towards the end of the first volume or start of the second volume -- surprisingly often, that’s the point where inspiration seems to fade and contractual obligations to take over. It's as if, in Lewis Hyde's terms, the “labor” or vocational endeavor ends and the “work” or professional endeavor kicks in. Walton’s Small Change or Still Life With Fascists trilogy is unfortunately not an exception to this natural law.
As long as we remain within the world of the country house, the politics of Walton's world are entirely believable – a 1930s country house full of people who rather sympathize with Hitler is perfectly plausible. What strains credulity is that such politics could be imposed on the whole country, meeting no serious resistance, without the Nazis even having to occupy England. John Clute has already made this point.
The way Walton parodies the Mitford family in Ha'penny is fun. Unfortunately the guiding thesis of the trilogy overall seems to be that signing a peace treaty with an evil power has identical moral consequences to being subjugated by an evil power. This thesis isn't altogether true, and the trilogy suffers from this. However, provided you read it as a standalone book, disregarding the sequels, Farthing is an excellent read.