Unnatural Death was published in 1927 and is the third Lord Peter Wimsey novel. The setup is one of the cleverer in the series. A country doctor named Carr tells Lord Peter at a dinner that he is certain a wealthy elderly patient of his, Agatha Dawson, was murdered, although her death looked entirely natural. There is no medical evidence of foul play. There is no apparent motive. The case has been closed.
Peter and his friend Miss Climpson, an elderly investigator he has set up in a London agency specializing in inheritance cases, begin to trace the financial implications of the death. The eventual unraveling depends on a piece of British inheritance law that Sayers takes seriously and explains in genuine detail, plus a method of murder that does not show in autopsy and that requires the perpetrator to have specific medical training. Miss Climpson’s letters home are some of the funniest material Sayers ever wrote. The book turns on a moral question: is a killing still wrong if the victim was already dying? Sayers thinks it is.