The opinion that there was little to choose between communism and fascism, and that the two kinds of dictatorship are equally reprehensible, is given special prominence by being attributed to Lord Peter Wimsey himself.
The papers do provide some significant new details about Wimsey's character, in particular the ironic epitaph he writes for himself when setting out for a dangerous mission behind enemy lines: Here lies an anachronism in the vague expectation of eternity.
They also show that in addition to his thorough knowledge of the classics of English literature, Wimsey is familiar – though in fundamental disagreement – with the works of Karl Marx, and well able to debate with Marxists on their home ground.
The letters provided much information which Walsh used in the book: Peter Wimsey and his servant Bunter being on a secret mission abroad, Harriet Vane taking her own children and those of her sister-in-law Mary to the country house Talboys in Hertfordshire, Peter's nephew Jerry an RAF combat pilot, and the unsympathetic Duchess Helen working at the Ministry of Instruction and Morale (about whose work Sayers was rather disparaging).
The village dance and air raid practice, which are the starting point for the plot of A Presumption of Death, are also derived from one of Sayers' fictional letters, though the idea of making this the scene of a murder to be investigated was Walsh's.