Wikipedia page about this book: https://en.wikipedia.org/wiki/The_Circular_Staircase

Release date is 1996-02-01

"The Circular Staircase" by Mary Roberts Rinehart is a mystery novel published in 1908. When Rachel Innes rents a country house for the summer with her niece and nephew, she encounters mysterious intruders, unexplained noises, and a murder at the bottom of the titular staircase. As bodies accumulate and secrets multiply, Rachel must untangle a web of hidden identities, missing money, and family betrayals. This pioneering work established the "had I but known" mystery formula and became Rinehart's first bestseller. (This is an automatically generated summary.)

Original publication data not identified