What is the theme in Whose Body?: A Lord Peter Wimsey Novel by Dorothy L. Sayers?

Jealousy is the motive for the crimes that occur in this story. Freke, as is revealed over the course of the story, is jealous of Levy because Levy's wife, Christine, had originally been somewhat involved with Freke. The Dowager Duchess says that Christine had initially been involved with Freke though it was more of a situation in which her parents approved of the match. When Christine chooses Levy over Freke, Levy has yet to make his fortune. Her family is, according to the Dowager, upset though the Dowager says that Christine had likely made the correct decision, choosing love over her family's choice. While Peter says that it is impossible to believe that Freke would have harbored jealousy for the twenty years after the fact, Peter says that Freke would have harbored an even more passionate form of the emotion—humiliation at having been rejected in favor of a man who Freke clearly considers inferior.