Team Rocket are dragging their feet on the road. Suddenly, a Magikarp is thrown to James. James looks ahead and sees the Magikarp salesman trying to sell him a Magikarp and Feebas. James demands that he won't be tricked this time, and he orders for his money back from his other scams. The Magikarp salesman then asks James if he is interested in the next big thing. James wonders what that is, and the salesman pulls out a cardboard box. The salesman explains that a powerful evolution machine is inside the box. He explains that his crew has been working on the machine for a long time by using the top technology ever. However, his company became bankrupt, so now he has the machine. Inside the cardboard box is an instruction manual and some accessories for building the machine. The salesman says that the machine they build will guarantee Pokémon evolution or their money back. Team Rocket is excited about this, and James takes it. The salesman tells them not to use the machine until a week after it is built, then he runs away.

Meanwhile, Ash and co. are continuing their way towards Floaroma Town for Dawn's next Pokémon contest. Their journey takes them into Jubilife City again. A couple walks up to Ash and co. The woman asks Ash if he would ever evolve his Pikachu. When Ash says no, the woman assumes that Ash is part of the B Button League. Dawn asks about the league, and the woman states that the league is where top coordinators compete without evolving their Pokémon. She explains that it is also home of the strongest Magikarp and Feebas. Then the woman leads Ash and co. to the building. Ash and co. walk inside, and two people greet them. They ask Ash and co. if they would like to join the league. Ash first wants to know what they do in the league. The girls introduce themselves as Haley and Arley. Then Ash and co. introduce themselves to the girls.

The girls lead Ash and co. into a big room. In the middle of the room lies a large water tank. The strongest Magikarp and Feebas are in the tank. Ash and Dawn look up the Pokémon in their Pokédex. The girls explain that the members of the B Button League believe that there is more to Pokémon than evolution, so the members train their Pokémon without evolving them. Ash totally agrees with them. He asks Arley if she would have a battle with his Pikachu. Dawn then asks if she would have a battle with her Piplup. Dawn never had the chance to see Piplup battle in water, so now would be the perfect time. Ash is anxious to see Piplup battle in water, too, but he doesn't know if Piplup will be powerful enough to take down Magikarp. Dawn is confident in herself, and she sends out Piplup.

Suddenly, Team Rocket walks in the room with disguises on. They claim that they are from the C button League. They plan on doing some investigation. Arley and Haley tell Team Rocket that they can stay while Arley battles Dawn. Dawn sends in Piplup to battle. Team Rocket plans on snatching Pikachu and then testing it out in their evolution machine. Piplup starts the battle off with Peck. Dawn notices that Piplup is fast in the water, too while it chases Magikarp. Magikarp dodges the attack by jumping high out of the water. Piplup then uses Bubblebeam. Magikarp dodges the attack one more time and uses Tackle. The Tackle attack from Magikarp was way too powerful for Piplup, and Piplup ends up fainting.

Now it is Ash's turn to battle. Dawn states that Magikarp has to be weak against electric attacks no matter how powerful it is. Pikachu starts off with Thunderbolt, but Magikarp dodges it. Then Magikarp jumps into the air and uses Tackle. The force from Magikarp's body slides Pikachu to the edge of the pool. Jessie wonders how powerful Magikarp would be if it evolved into Gyarados. She tells James that they are going to steal Magikarp instead for a test run. Pikachu then uses Quick Attack, and Magikarp uses Tackle. Both Pokémon collide into each other, and then they fall into the pool. Ash notices that Arley's Magikarp is very strong.

Team Rocket walks up to Ash and co. They tell them that they plan on putting Arley's Magikarp on the front page newspaper. They want to get a few pictures of Magikarp. While they are doing that, Ash and Dawn compliments on Arley's Magikarp. Haley was hoping that they would get to see her Feebas in action. Ash and Dawn are sure that Haley's Feebas is just as strong. Then they turn around and see Team Rocket placing Magikarp and Feebas in a bag. When they are spotted, they say their motto. Arley and Haley demand for their Pokémon back. When Team Rocket refuses to give back the Pokémon, they run away with Ash and co. chasing them. Team Rocket flies away in their balloon. Ash sends out Staravia to try and catch up with Team Rocket.

Staravia comes back and reports to Ash and co. to follow it. Staravia leads them to a small house. They open the door to see Team Rocket with their evolution machine. Inside the machine are Magikarp and Feebas. Team Rocket plans to force the Pokémon to evolve. Haley and Arley plea to Team Rocket not to evolve their Pokémon. Ash tells Pikachu to use Thunderbolt, but a cage is locked on Pikachu before the attack is released. Then a cage drops on Ash and co. to prevent them from escaping or ruining their plans. The cage that contains Magikarp is lowered into the machine. The machine turns on and a light flashes. However, Magikarp drops out of the cage. It has not evolved! James and Meowth look at the manuals again, wondering if something went wrong. They try the evolution process again, but it still doesn't work. Team Rocket decides to lower Pikachu in the machine instead. Unfortunately for Team Rocket, the machine doesn't work on Pikachu either. Meowth finds out that it may take up to a week for the machine to work, otherwise it will fail. This gets Jessie angry.

Pikachu uses Iron Tail to break the cage, freeing Ash and co. Ash tells Team Rocket that they are finished. Meowth stops him, and says that the evolution machine can transform into a Mega Bot. Meowth presses a button on the remote. The evolution machine is launched into the air and it transforms into a huge robot. However, within seconds the robot falls apart. Meowth states that an evolution has to successfully take place for the robot to work. James thinks they were ripped off again. Now it's time for Arley and Haley to teach Team Rocket a lesson. Magikarp first uses Tackle on Team Rocket, and Feebas uses Ice Beam to freeze them. Finally, Pikachu uses Thunderbolt on Team Rocket, blasting them off again.

Arley and Haley are glad that their Pokémon haven't evolved. Then they wave goodbye to Ash and co. as they head off towards Floaroma Town for Dawn's next Pokémon contest.