The Circular Staircase by Mary Roberts Rinehart

Mary Roberts Rinehart was a prolific writer that is often referred to as the American Agatha Christie.  Rinehart's mystery novels are still treasured by millions of readers today and she is the source of the famous phrase "The butler did it."  Rinehart's most famous books include The Circular Staircase, The Bat, The Case of Jennie Brice, and The Door.

The Circular Staircase, published in 1908, tells the story of Rachel Innes, a spinster who fights off a series of mysterious crimes at a summer house she has rented with her niece and nephew.  The book is considered to be Rinehart's greatest work and has been turned into film and a classic Broadway play.