The Circular Staircase

A middle-aged spinster loses her mind and finds herself involved in a most mysterious crime.
Rachel Innes ignores her better judgment and rents Sunnyside, a sprawling Elizabethan mansion, for the summer. The first night passes peacefully. In the morning, the entire staff quits. Late the third night, a sinister figure lurks outside the patio window and Rachel hears a heavy crash on the staircase. The fourth night brings a dead body.
The dead man turns out to be Arnold Armstrong, ne'er-do-well son of the owner of Sunnyside. When the investigating detective directs his attention to her niece and nephew, Rachel decides to solve the murder herself – and walks straight into a web of deceit and treachery so intricate she might never find her way out.