Dumb Witness By Agatha Christie

Everyone blamed Emily Arundell’s accident on a rubber ball left on the stairs at her home in Market Basing by her frisky terrier, Bob. But the more she thought about her fall, the more convinced she became that one of her relatives was trying to kill her.

So, on April 17th she wrote about her anxieties and suspicions in a letter to Hercule Poirot. And included a request that he consult with her as soon as possible. Mysteriously he didn’t receive the letter until June 28th … by which time Emily was already dead.