The Circular Staircase by Mary Roberts Rinehart is her first published novel and was wildly popular when it first came out in 1907. It catapulted the 27 year old ex-nurse into national fame and she kept her family in relative luxury through several more best-selling novels. The Circular Staircase is a gripping mystery story and one that's guaranteed to keep readers guessing till the very end. It is also the book which invented the "Had I But Known It" school of detective fiction, in which the principal character's actions have the effect of inadvertently prolonging the mystery and the action. Ogden Nash famously parodied this form of mystery writing in his poem Don't Guess Let Me Tell You: "Had I but known what I know now, I could have saved at least three lives by revealing to the Inspector what I heard through that fortuitous hole in the floor!"
