"Unnatural Death" by Dorothy L. Sayers is a mystery novel published in 1927. Lord Peter Wimsey investigates the seemingly natural death of an elderly cancer patient, despite no evidence of foul play. When witnesses begin dying mysteriously and a closer relative surfaces who would inherit under new property laws, Wimsey uncovers a chilling pattern. With help from private investigator Miss Climpson, he pursues a cunning killer using an ingenious murder method—but the trail leads to unexpected connections and deadly disguises.
Wikipedia page on this work: en.wikipedia.org/wiki/Unnatural_Death_(novel)) Also published under title: The Dawson pedigree