The Circular Staircase was written in 1908 by Mary Roberts Rinehart, a woman many considered to be the "American Agatha Christie." This particular novel is one of the first mysteries in the "Had I but known" style, in which the first person narrator is telling the story from a point after the events, and often throws in small hints about the danger that is to come.
In this particular case, Rachel Innes--a middle-aged spinster--decides to take a house in the country for the summer, along with her niece and nephew, whom she has raised for most of their lives. The house, Sunnyside, turns out to have some very strange issues, including many suspicious things that go bump in the night. As if that wasn't bad enough, shortly after they arrive, a man is shot in the house during the night, even though all the doors were closed and locked. Soon, both of Miss Innes's wards are wrapped up in the mystery, and the house continues to be haunted by noises and uninvited guests. Miss Innes, along with Detective Jamieson and the comedic maid Liddy, manage to untangle the deadly mystery.
This is not a bad book, and the mystery was logical but not easily figured out. Some of the dialogue was funny, and the characters were relatively well-written. One thing that I did find a bit disconcerting was the casual racism throughout the book. The character of Thomas the butler is written as a blatant Uncle Tom stereotype, and the other characters make flippantly disparaging remarks--i.e., using the word "darkies" and discussing their tendency toward laziness, stupidity, and inability to handle money--in passing conversation. It's not unusual, I suppose, for the time the book was written, but it feels very strange now that a character in a book can be nonchalantly racist. Nowadays, racism is used as an indicative character trait, not just some conversational filler.
Aside from that small issue, this is a tolerable book, though it's nothing special.