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 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.

The Circular Staircase is a mystery novel by American writer Mary Roberts Rinehart. The story follows dowager Rachel Innes as she thwarts a series of strange crimes at a summer house she has rented with her niece and nephew. The novel was Rinehart's first bestseller and established her as one of the era's most popular writers. The story was serialized in All-Story for five issues starting with the November 1907 issue, then published in book form by Bobbs-Merrill in 1908.