Ash and his friends enter a small town where all the girls are lined up to watch Aaron, one of the Elite Four, conduct a public training session. Aaron knows his Bug-type Pokémon so well, he can even understand what Bug-type Pokémon say. Aaron plans to challenge Cynthia for the top Trainer spot in Sinnoh, and the crowds are certainly impressed by his Vespiquen, Drapion, and Skorupi. When Aaron learns that Dawn and Ash know Cynthia, he takes them to his private training center in the woods. Team Rocket follows them and puts syrup on a tree to lure Aaron's Pokémon, but it only ends up attracting Beedrill!

Dawn notices a photo of Aaron and a Wurmple. This Wurmple was Aaron's greatest friend, but Aaron doesn't seem to have a Wurmple now—where did it go? Before Aaron can explain, Team Rocket's balloon descends from the sky and vacuums up his Pokémon along with Pikachu and Piplup. Team Rocket escapes, but Aaron is determined to find and rescue his Pokémon. When he was young, he was a poor loser who blamed Wurmple for his defeat, driving Wurmple away. Ever since that mistake, he's worked hard to understand Bug-types and vowed not to lose a Pokémon ever again!

Team Rocket doesn't get far—their kidnapped Pokémon decide to fight back, and the balloon crashes in the forest. As Seviper and Carnivine try to stop Pikachu, Piplup, and Aaron's Pokémon from escaping, Aaron and our heroes arrive to save the day. Team Rocket makes a second attempt to vacuum up the Pokémon, but a Beautifly stops them with a powerful SolarBeam attack. Team Rocket crashed near the tree where Aaron met Wurmple, and this Beautifly is the Evolution of Aaron's Wurmple! All this time, it's been training to become strong enough to help Aaron. Now it's certainly strong enough to help defeat Team Rocket, and Team Rocket is sent packing by the combined attacks of our heroes' Pokémon. As Aaron happily trains for his big challenge, Ash heads to Hearthome City for his own big challenge: a Gym Battle against Fantina!