On the way to the Grand Festival, our heroes are swarmed by a group of Aipom who swipe Ash's hat and May's ribbon case! That's not all—the Aipom also cleaned out an orchard belonging to a farmer, Taylor. He says the local Pokémon have started acting strangely, and it might have something to do with a strange monster recently seen in the mountains. Everyone sets out to investigate and get May's ribbons back.
Up in the mountains, the Aipom have brought their loot as a tribute to the monster, a Mountain King who's represented by none other than Team Rocket. Ash and his friends show up and challenge them, but then the Mountain King appears: a giant Slaking! Team Rocket orders the Pokémon to chase off our heroes in the name of the Mountain King, and everyone splits up to get away. In the commotion, Ash saves the Aipom who took his hat, then runs off and to find his friends.
Ash and his friends regroup and confront Team Rocket, but their giant Slaking grabs May! Ash's Pokémon get her to safety and Combusken's flames burn the Slaking to reveal that it's a giant robot. Aipom shows up with the other Pokémon and help wreck the robot now that Team Rocket's tricks have been revealed. Then it's just a matter of convincing Team Rocket to return May's ribbons and leave the scene—with encouragement from Combusken and Pikachu. Taylor gets his Berries back and Ash gets his hat... as well as a new fan!