The Circular Staircase by Mary Roberts Rinehart

Published in 1908, this was Rinehart's first bestseller and the novel that established the "had-I-but-known" school of mystery writing. A spinster and her niece and nephew rent a country house for the summer and find themselves at the center of a string of increasingly strange crimes.

Includes the full unabridged audiobook (LibriVox recording) along with the ePub.