In Dumb Witness by Agatha Christie, Emily Arundell, a wealthy spinster, writes to Hercule Poirot believing she was the victim of attempted murder after a fall in her home. Her family and household believe she fell by accident, after tripping over a ball left by her fox terrier Bob. The more she thought about her fall, the more convinced she became that one of her relatives was trying to kill her.

However, her letter is delayed and when Poirot receives it, she has been dead for some time. Her doctor says that she died of liver problems she had had for many years.

Poirot investigates the suspicious death of Emily, who, fearing the very worst, had written to him prior to her demise. Through a number of cover stories Poirot converses with those who knew Emily, finding out more about the people involved and the events leading up to her final illness. But Poirot fears that the killer has not finished just yet.