Dorothy L Sayers' detective fiction output was not large. From the total of eleven novels, two at least have never been regarded as highly by critics and readers as have the others. "Murder Must Advertise" is one of them.
Re-reading it recently, I decided that most of its weaknesses are less apparent if it is treated as a light entertainment. Why should I expect the scholarly Miss Sayers to always provide verisimilitude, evidence of thorough research and scientific investigation? It soon becomes clear, in this book, that the pukka, debonair Lord Peter Wimsey is highly unlikely to be doing a stint as an advertising copywriter, that he would be fool enough to dive from a great height into a fountain, and that a murder such as the one he is investigating could ever be committed.
Deciding not to take these things seriously, I enjoyed my time with the book, especially the description of Lord Peter Wimsey winning the cricket match for his advertising agency. It became impossible, however, at the end to regard the book as light entertainment. The tone changes. Miss Sayers is forced to meet the problem of dispensing justice to the killer, once identified. Her solution is heavy-handed.
Ah! well, many whodunits have disappointing endings. Approach this one as I have suggested, and you'll enjoy most of it. Don't expect Harriet Vane to feature, however. Dorothy L Sayers never mentions her by name, only referring to the woman in Lord Peter's life who is being "deliberately excluded from these pages".