The Circular Staircase by Mary Roberts Rinehart
The Circular Staircase is the first of Mary Roberts Rinehart's novels I've read. I don't know why it has taken me so long to get around to reading her.
The Circular Staircase is apparently the first example of the "Had-I-But-Known" school of mystery writing. The Had-I-But-Known mystery novel is one where the principal character (frequently female, in this case Rachel Innes) does things in connection with a crime that have the effect of prolonging the action of the novel. Ms. Innes keeps information from the police, does her own investigation, actively hides things the police should know - basically she's a standard amateur detective. I take that back, she literally hides people, which is taking the whole thing a little far. Of course, she's surrounded by people who are keeping secrets too, but they are suspects, so that's expected.
So, Ms. Innes, her niece and nephew, and her maid move into a rented country house for the summer. The owners, a rich...