The Man in Lower Ten

Mary Roberts Rinehart (August 12, 1876-September 22, 1958) was a prolific author often called the American Agatha Christie. She is considered the source of the phrase ＂The butler did it＂, although she did not actually use the phrase herself, and also considered to have invented the ＂Had-I-But-Known＂ school of mystery writing.