Unnatural Death

Unnatural Death is a 1927 mystery novel by Dorothy L. Sayers, her third featuring Lord Peter Wimsey. It was published under the title The Dawson Pedigree in the United States in 1928.

According to James Brabazon in his Dorothy L Sayers: a biography (1981), Sayers drew her ingenious (and medically doubtful) murder method from her familiarity with motor engines, gained from her affair with a car mechanic and motor-bike enthusiast.
In their review of Crime novels (revised edn 1989), the US writers Barzun and Taylor stated that "The tale is perhaps a little forced in conception and remote in tone. That is the trouble with all the great masters - they accustom us to such dazzling performances that when they give us what would seem wonderful coming from other hands, we sniff and act choosy. The mode of compassing death has been carped at, but no one could do anything but rejoice at Miss Climpson and her subterfuges."
HRF Keating, writing in 1989, noted that Sayers had "invented a murder method that is appropriately dramatic and cunningly ingenious, the injection of an air-bubble with a hypodermic". However, "not only would it require the use of an instrument so large as to be farcical, but Miss Sayers has her bubble put into an artery not a vein. No wonder afterwards she pledged herself 'strictly in future to seeing I never write a book which I know to be careless'."

In Murder in the Closet: Essays on Queer Clues in Crime Fiction before Stonewall (2017), Noah Stewart described Mary Whitaker as being "to my knowledge the most clearly delineated homosexual character in Golden Age detective fiction, despite the word 'lesbian' never being used, and she's depicted as enticing a young girl into a life of homosexuality". The episode in which Mary Whittaker is kissed by Wimsey is "the closest that a writer in 1927 would be able to come to saying that a character was a lesbian and that kissing a man made her want to vomit." Laura Vorachek argued that, in the novel, "Sayers attempts to challenge the prevalent cultural associations of blackness and criminality."

In May 1975, an adaptation was made for BBC Radio 4, produced by Simon Brett and starring Ian Carmichael as Lord Peter Wimsey. (wikipedia.org)