Clever Willy and his young pirate friends Marie and Thomas go to Granny Island. There they are met by a family headed by grandfather - the Legendary Jacques. The latter is convinced that travelers are coming to the island to steal his treasure. However, no one could find it, not even Jacques himself, because the old pirate made a mistake while drawing a map of the treasure's location. The heroes do not lose hope and, having received the map, go in search of a treasure in a cave guarded by a dragon!