I'm sure most Fox Terrier fans have read "Dumb Witness" by Agatha Christie, in which the mystery is solved by a WFT called Bob, with the assistance of Poirot.
I was delighted to read about the recent discovery of two unseen Christie short stories which will be published by HarperCollins in autumn. One of these is called "The Mystery of the Dog's Ball", which was eventually re-worked into the novel "Dumb Witness".
"Secret Notebooks: Fifty Years of Mysteries in the Making" by John Curran will contain this and another never seen before short story, along with insights into how Christie worked, re-using ideas and developing plots.
Take a look at the official Agatha Christie website for more fascinating facts.