Mary Roberts Rinehart (August 12, 1876 – September 22, 1958) 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 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. She also worked to tell the stories and experiences of front line soldiers during World War I, one of the first women to travel to the Belgian front lines. Source: Wikipedia (en)