Professor Willow reports widespread sightings of Ditto transformed into an undiscovered Pokémon to Professor Oak, who recognizes the Pokémon from ancient texts as the Mythical Pokémon Meltan. Both of them team up to continue investigating the new Pokémon.

Professor Oak sends a mysterious box he found containing a rusty metal lump to Professor Willow. Upon opening it out in the field, the box summons a bunch of Meltan. However, not long after the box is opened, it closes again and cannot be re-opened for some time.

After Professor Willow has caught a lot of Meltan and updates Professor Oak on the new information he has discovered, the two professors notice that Meltan has transformed. Oak informs Willow that the Meltan have evolved into Melmetal, so Willow sends Melmetal to Oak's Laboratory, despite the fact that Oak tells him that the lab is not yet ready to receive it. Oak receives Melmetal, before Willow notices a stray Meltan and wonders if there are more amazing Pokémon like Meltan that are left to be discovered.