The Circular Staircase

Mary Roberts Rinehart was an American writer, often called the American Agatha Christie.Rinehart published her first mystery novel The Circular Staircase in 1908, which introduced the "had I but known" narrative style. Rinehart is also considered[by whom?] the source of "the butler did it" plot device in her novel The Door (1930), although the exact phrase does not appear in her work.