The Circular Staircase (Unabridged‪)‬

"This is the story of how a middle-aged spinster lost her mind, deserted her domestic gods in the city, took a furnished house for the summer out of town, and found herself involved in one of those mysterious crimes that keep our newspapers and detective agencies happy and prosperous." So begins
The Circular Staircase, a book which has been hailed as the best novel by the most important American woman mystery writer. Rachel Innes is relieved when Gertrude and Halsey arrive to keep their dear old aunt company and allow her the courtesy of a decent night's sleep. Unfortunately, the explosive sound of a revolver shot the next night shatters Rachel's hopes. And the body at the foot of the circular staircase insures many sleepless nights to follow.