Ash, Serena, and Bonnie are talking to Clemont via video phone, and Clemont introduces to them his newest invention: a machine that detects dirt and the like and automatically cleans it up. However, the machine mistakes Clemont for dirt himself, and it explodes as he tries to resist it. Soon after, Ash, Serena, and Bonnie continue their travels to Lumiose City. As Ash decides to train, he begins to think about possible strategies to counter Clemont's Pokémon. Suddenly, Tierno steps out from behind a tree and greets the three of them. After again expressing his admiration and affection for Serena, Tierno notices Clemont's absence, whereupon Ash explains that Clemont is the Lumiose Gym Leader. Tierno explains that he battled Clembot for his Voltage Badge and won, and then agrees to have a training battle with Ash.
In a clearing in the woods, Ash calls out Sliggoo to battle against Tierno. Tierno then shows Ash his team of Pokémon: a Politoed, Wartortle, Ludicolo, and Hitmontop, and Wartortle having evolved from his Squirtle. Ash and Tierno agree to have a Double Battle, with Tierno bringing out his Raichu to partner with Wartortle. Ash decides to have Pikachu partner with Sliggoo. Just before the battle begins, however, a strange machine rolls out of the bushes and grabs Pikachu. An automated message from Team Rocket plays from the mecha, bragging about it and explaining their newest attempt to capture Pikachu. As the mecha tries to drop Pikachu into a cage, Sliggoo uses Dragon Breath to force it to release Pikachu. Suddenly, however, it turns around and immediately grabs Raichu and Wartortle instead. While Pikachu is thrown off the moment he tries to help, Sliggoo manages to grab hold of one of the arms, but all three Pokémon are hurled into the cage and the device releases a pink gas to facilitate its escape.
While en route to where Team Rocket is waiting, Wartortle and Raichu try without success to break the bars of the cage while Sliggoo cowers, frightened. Meanwhile, Fletchinder searches without success for the mecha, and the group splits up to continue searching. Ash and Serena head one way, while Tierno and Bonnie head the other way. When the mecha arrives at where Team Rocket is relaxing, Jessie, James, and Meowth are dismayed to discover that it had responded to Raichu's internal electricity instead of Pikachu's and had captured the wrong Pokémon. Raichu and Wartortle attack James and Jessie from inside the cage, and Jessie responds in kind by having Pumpkaboo attack them. However, the Shadow Ball hits the line connecting the cage to the machine and the cage rolls away with Raichu, Wartortle, and Sliggoo still inside it. Jessie then apathetically orders the mecha to resume its search for Pikachu.
Tierno and Bonnie work their way through very thick grass in their search for the missing Pokémon. Suddenly, the cage falls over the cliff next to them and they discover the three Pokémon, stunned from the crash. After making sure that their friends are all right, Tierno and Bonnie realize that the mecha is probably still after Pikachu. Bonnie asks Dedenne to find Pikachu, and Dedenne begins leads them in the right direction by using its electricity to sense Pikachu's location. Bonnie and Tierno, while following Dedenne, come across a giant rock. Tierno is amazed at Sliggoo's determination to destroy it and has Raichu and Wartortle help it, thus removing the obstacle. Meanwhile, Ash, Serena, and Pikachu are still searching for the three missing Pokémon when Dedenne's electricity reaches Pikachu. Before they can go to find Tierno and Bonnie, however, the mecha reappears and Pikachu drives it away with Iron Tail before he, Ash, and Serena flee while they can. While they are being chased by the machine, it manages to grab Pikachu again. Just in time, Sliggoo arrives and tackles the mecha, preventing Pikachu from being caged. However, as Jessie has Pumpkaboo use Shadow Ball again, it hits the mecha and destroys it, causing sparks to fly everywhere and starting a massive fire.
While Ash, Serena, Pikachu, Sliggoo, and Team Rocket are surrounded by a ring of flames, the fires trigger several painful memories in Sliggoo of its friends being hurt when its homeland was attacked. In response, Sliggoo uses Rain Dance and summons a storm to put out the fire, triggering its own evolution into Goodra as well. Seeing the power of Ash's new Pokémon, James suggests that they attempt to capture Goodra instead, but his plain is short-lived. Despite opposition by both Pumpkaboo and Inkay, Goodra uses Dragon Pulse to easily send Team Rocket blasting off. With Team Rocket out of the way, Ash and Tierno resume their battle. After using a combination of Iron Tail and Bide to counter Tierno's strategy of Focus Blast and Rapid Spin, Ash breaks through Tierno's dance rhythm and wins the match.
That evening, Ash, Serena, and Bonnie say goodbye to Tierno and finally arrive in Lumiose City, excited for Ash's battle against Clemont.
