Professor Oak has finished his research on the mysterious Pokémon Ash reported on and discovered it's the Mythical Pokémon, Meltan. One of the Meltan has grown attached to Ash's Rowlet and joins them all at the Pokémon School, but after an incident, its nut gets stolen. The group tries to replace it but it doesn't fit so Meltan and Rowlet head out to find its old nut. However, while hunting, they bump into Team Rocket who are still after all the Meltan. Will they be able to protect Meltan?