On the way to meet Clemont in Lumiose City, our heroes run into their friend Tierno from summer camp! A Team Rocket robot quickly interrupts the happy reunion when it grabs Ash’s Sliggoo and Tierno’s Raichu and Wartortle, and then carts them back to the villains. But Jessie is annoyed that their “Automatic Pikachu Catcher” malfunctioned and sends it flying, allowing the Pokémon to escape.
When Team Rocket comes after Pikachu again, Sliggoo bravely steps up to protect it. When their robot explodes and starts a fire, Sliggoo evolves into Goodra to put out the flames with a powerful Rain Dance before sending the villains blasting off again!
Finally, Ash and Tierno get to have the Double Battle they’ve been planning. Raichu and Wartortle are formidable opponents, but the team of Pikachu and Goodra proves too much for them, and Ash wins! Tierno wishes Ash luck in his upcoming Gym battle and heads off to continue his own journey, and our heroes finally have Lumiose City within their sights!
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 he 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, with 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 using Thunderbolt and Water Gun, respectively, and Jessie responds in frustration by having Pumpkaboo attack them with Shadow Ball. However, the attack 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 to lead them in the right direction by using its electricity to sense Pikachu's location. Bonnie and Tierno, following Dedenne, come across a giant rock. Sliggoo tries to destroy it with Dragon Breath, but its attacks make little progress. Tierno is amazed at Sliggoo's determination to destroy it and has Raichu and Wartortle help, 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, the machine manages to grab Pikachu again until Team Rocket appears. Just in time, Sliggoo arrives and tackles the mecha, preventing Pikachu from being caged. However, as Jessie sends Pumpkaboo to 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 plan is short-lived. Despite the blows by Pumpkaboo and Inkay's Dark Pulse and Psybeam, Goodra uses Dragon Pulse to easily send Team Rocket blasting off.
With Team Rocket out of the way, Ash and Tierno resume their battle. Pikachu uses Quick Attack while Wartortle holds its ground and use Rapid Spin. Pikachu manages to dodge while Raichu uses Charge Beam and Focus Blast on Goodra, but Goodra takes the hit and begins charging Bide. Although Pikachu tries to counter another Focus Blast with Electro Ball, Wartortle interferes with another Rapid Spin and allows Raichu to successfully execute its attack. With its Bide fully charged, Goodra launches the attack and Wartortle tries to block with Hydro Pump, but Pikachu responds with Iron Tail, allowing Goodra's Bide to hit Raichu and Wartortle. Tierno and his Pokémon then begin their dance rhythm and Wartortle uses Skull Bash, but Goodra catches and holds Wartortle. As Raichu tries to use Focus Blast, Pikachu counters it with Electro Ball again. Goodra throws Wartortle into Raichu, leaving them both struggling. To finish off their opponents, Pikachu uses Thunderbolt on Wartortle and Goodra uses Dragon Pulse on Raichu. Both attacks hit the Pokémon, knocking them out, and Ash is declared the winner of the battle.
That evening, Ash, Serena, and Bonnie say goodbye to Tierno and finally arrive in Lumiose City, excited to see Clemont again and for Ash's battle against him.