Mary Roberts Rinehart 
The Circular Staircase 

Fans of golden-age mystery fiction, you're definitely in for a treat. This novel has it all: skillful writing, a drum-tight plot, and snappy, witty dialogue. The Circular Staircase is about Rachel Innes, a well-to-do woman of a certain age. Her Pittsburgh manse is in need of an overhaul, so she decides to spend some time at the country home of a friend to escape the hustle and bustle of the remodeling process. But what appears at first to be a quaint rural outpost soon reveals itself to be the epicenter of a beguiling puzzle.