Summary: Initially, this book presents itself as a classical English murder mystery, set in the late forties: A dozen guests are spending a weekend at the country home of a wealthy aristocrat. One of them, a distinguished politician, is found dead one morning, under circumstances that strongly suggest that one of the other guests murdered him. An inspector is called in from Scotland Yard to make inquiries.

Only a few pages into the book, however, the reader is confronted with a disconcerting oddity:

“You know, in Germany --” Daddy began.

“But we're not in Germany. We fought a war -- you and David both fought a war -- to ensure that the border of the Third Reich stops at the Channel. It always will. Germany doesn't have anything to do with anything.”

This offhand description of the purpose of the Second War comes as a shock, quite dissonant with the conventions on which the author seemed to be relying. The reader soon discovers that this is an alternate-history novel, one in which Rudolf Hess's 1941 mission was successful.

Hess was one of Hitler's deputies. In May 1941, apparently on his own initiative, he flew into Britain to try to negotiate a peace treaty, or at least a truce, that would enable Germany to fight the Soviet Union without having to worry about a Western front. In the real world, he was arrested and imprisoned; after the war, he was tried at Nuremberg and sentenced to life imprisonment. In the Farthing universe, however, he managed to reach a member of Parliament who took up his offer, and, within a month, Britain and Germany had reached a settlement that left Germany in complete control of continental Europe.

The murder victim is the member of Parliament who led the negotiations that resulted in this treaty. He is now the Minister for Education in a right-wing Conservative government. The Scotland Yard inspector soon determines that the circumstances of the murder have been staged, in an almost comically crude way, to throw suspicion on the victim's political opponents, more specifically on British Jews, and most specifically of all on the aristocrat's son-in-law, who happens to be Jewish.

Step by step, the conventional murder mystery recedes (although it is resolved in the end), giving way to a cautionary tale about politics and terrorism. The author's epigraph turns out to be an accurate indication of the tone she achieves:

This novel is for everyone who has ever studied any monstrosity of history, with the serene satisfaction of being horrified while knowing exactly what was going to happen, rather like studying a dragon anatomized upon a table, and then turning around to find the dragon's present-day relations standing close by, alive and ready to bite.

The novel gives this experience both to the characters and to the reader.