Dumb Witness by Agatha Christie

A simple accident?
Or attempted murder?

Everyone blamed the dog. When a wealthy spinster trips on the stairs, it seems only natural to assume it was an accident – a rubber ball left there by her lively terrier.

And yet the more Emily Arundell thought about it, the more convinced she became that one of her relatives was trying to kill her. Seeking answers, she writes to the famous detective, Hercule Poirot.