The Circular Staircase (1908) is a mystery novel in the ‘Had I but known’ genre by American author Mary Roberts Rinehart. She wrote the book, which became her first best-seller, at her home at 954 Beech Avenue in Allegheny, Pennsylvania, now part of Pittsburgh.The ‘HIBK’ genre is associated with several works of Rinehart, specifically The Circular Staircase, in which ‘a middle-aged spinster is persuaded by her niece and nephew to rent a country house for the summer. The house they choose belonged to a bank defaulter who had hidden stolen securities in the walls. The gentle, peace-loving trio is plunged into a series of crimes solved with the help of the aunt. This novel is credited with being the first in the ‘Had-I-But-Known’ school.’