After Fievel has another escapade with Tiger in Green River, Papa "Bernard" Mousekewitz decides to tell his children of how he met Mama and what adventures he had with her in Shostka when he was kidnapped by an organisation of cats with far more sinister plans installed.
Link: https://www.deviantart.com/sebigraphart/journal/The-Book-of-Bernard-Mousekewitz-is-now-complete-1133803510
