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, when 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. Serena checks her Pokédex on Raichu. Ash decides to have Pikachu partner up 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 when 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. Even Raichu's Thunderbolt is useless and it ended up hitting Wartortle instead. Sliggoo, who cowers in the cage, worried. 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 with Thunderbolt and Water Gun, and Jessie responds in anger by having Pumpkaboo attack them with Shadow Ball. 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 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 run off while following Dedenne. 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 stops it with Iron Tail before he, Ash, and Serena run off while they can. Back with Bonnie and Tierno, they come across a giant rock. Sliggoo tries to destroy it with Dragon Breath, but no luck until it starts pushing the rock aside. Tierno is amazed at Sliggoo's determination to destroy it and has Raichu and Wartortle help it, thus removing the obstacle.
While Ash, Pikachu and Serena are being chased by the machine, it manages to grab Pikachu again until Team Rocket shows up. Just in time, Sliggoo arrives and tackles the mecha, preventing Pikachu from being caged until Bonnie, Tierno and the Pokémon appeared. However, as Jessie sends Pumpkaboo once again to use Shadow Ball and Pikachu and Sliggoo dodge the attack, 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. Ash was impressed when Goodraq used Rain Dance to put out the fire. Jessie is unhappy about getting wet again while James suggests they capture Goodra. But Jessie states they don't need Goodra but to teach the heroes a lesson. They send Pumpkaboo and Inkay to use Dark Pulse and Psybeam, but Goodra steps in and absorbs the attacks. Ash orders Goodra to use Dragon Breath, but Goodra use another attack better and easily send Team Rocket blasting off. Tierno explains to Ash that Goodra didn't use Dragon Breath but it used Dragon Pulse instead. Ash was happy that Goodra learned a new move.
With Team Rocket out of the way, Ash and Tierno resume their battle. Pikachu starts off with Quick Attack while Wartortle holds it ground and use Rapid Spin. Pikachu manages to avoid. Raichu uses Charge Beam and Focus Blast on Goodra, but Goodra took the hit and uses Bide while charging up. Tierno tells Raichu to use another Focus Blast, but Ash tells Pikachu to block with Electro Ball, but before Pikachu can use the attack, Wartortle steps in and hits him with Rapid Spin, allowing Raichu to hit Goodra with Focus Blast. Fully charged with Bide, Goodra launches the attack and Wartortle tries to block with Hydro Pump, but Pikachu blocks it with Iron Tail allowing Goodra's Bide to hit Raichu and Wartortle. Tierno allows his Pokémon to use their dance rhythm and tells Wartortle to use Skull Bash, but Goodra blocks the attack and holds Wartortle. As Raichu tries to use Focus Blast, Pikachu blocks it with Electro Ball. Goodra throws Wartortle into Raichu, leaving them both struggling. Using this as their chance, Ash tells Pikachu to use Thunderbolt on Wartortle and Goodra to use Dragon Pulse on Raichu. Both attacks hit Tierno's Pokémon, knocking them out and Ash wins the match.
Later, Ash, Serena, and Bonnie say goodbye to Tierno and tells to keep in touch with Shauna and Trevor. When its nighttime, the heroes finally arrive in Lumiose City, excited not only to see Clemont again, but for Ash's Gym Battle against him.
