Peril at End House by Agatha Christie
Peril at End House is classic Poirot. Lovely Nick doesn't know her life is in danger until Poirot helpfully points out that her near-accidents were probably not coincidence. But why would any of her friends want her dead? She's not rich, she's not mean. Poirot is determined to keep her safe, but that's easier said than done, especially when another woman is killed, mistaken for Nick.
This was a fun little mystery. The denouement was a good one, a bit unusual for a Poirot mystery. I mean, there was the typical gathering of all the players, but the excuse he uses to bring them together is a good one. The killer doesn't see the trap he has set at all. (S)he thinks (s)he has everyone fooled. (S)he doesn't, of course, and there are plenty of clues sprinkled through the book - I just missed them....