The Moving Finger by Agatha Christie. Miss Marple saves the day when poison-pen letters lead to a murder.
Sad Cypress by Agatha Christie. The first Agatha Christie I ever read. I was blown away by the way she plotted herself out of a seemingly airtight murder. Hercule Poirot reveals the defendant to be innocent and another person (someone you would never think of!) to be the murderer.
