Agatha and GKC

In 1939 Agatha Christie published a collection of murder mysteries with the title The Regatta Mystery. The volume included the cases of several of the author's detectives. In her notes, Christie describes as a "G.K.C. idea" the basic conception for the Miss Marple story in the collection. The idea, obviously based on Chesterton's 1911 story "The Invisible Man," was that the criminal is disguised as a housemaid—so no one notices her. [Janet Morgan, Agatha Christie, New York: 1985, p. 221]