Jim and his trusty mouse companion, Gran, toil tirelessly as innkeepers, yearning for a life at sea aboard their own vessel. Their mundane routine is disrupted when a stranger arrives at their inn, entrusting them with a map to the legendary Treasure Island. Determined to seek their fortunes, Jim and Gran embark on the ambitious task of constructing their boat for a treasure-hunting voyage. However, their quest takes a perilous turn as they encounter a band of ruthless pirates under the command of the infamous Captain Silver. With Silver coveting the treasure for himself, it falls upon Jim, Gran, and their newfound ally Kathy to outwit the treacherous captain and claim the coveted riches.