As other reviewers have mentioned, what makes this novel stand out from the usual period crime fiction is the portrayal of between-the-wars London when Armistice Day is still a real reminder of what men endured, when survivors of the first world war still suffer from shell-shock and the after-effects of gassing and wounds, and when having a wife go out to work is a significant slur on a man's masculinity.
The actual murder itself is less satisfying than some of the other novels in this series, and the unveiling of the culprit is a bit of a deux ex machina ending, so in some ways this works best as a novel with an incidental crime rather than the other way round. A good read anyway, though with a significantly darker centre than some of the other Wimsey books.