Everyone is relaxing on the beach as the episode opens. Ash is taking care of his Poké Balls and May is worrying about why her Wurmple isn't eating. Corphish, Ash's new Pokémon, is nibbling on some seaweed and starts to eat some rope before Ash can stop it. Team Rocket appears and snatches Pikachu. Wurmple uses String Shot to try and stop their balloon while Ash and company pull on the string to stop Team Rocket's escape. When Corphish tries to help, though, it snaps the string with its claws.
Ash and the gang hunt down the balloon and a fight ensues between the two groups to regain Pikachu. After Pikachu is back in Ash's arms, May and Jessie begin to argue (again) about whose Wurmple is better. To everyone's surprise, both Wurmple evolve. May's evolves into a Silcoon and Jessie's evolves into a Cascoon. Jessie thinks that hers is also a Silcoon, though. After another failed attempt at trying to catch Pikachu, Team Rocket is sent blasting off again. Corphish faints at this point and Ash realizes he has to rush it to the nearest Pokémon Center. Along the way, he must cross a large river guarded by a school of aggressive Carvanha. Seeing no other way to cross and with Corphish's condition worsening, Ash decides to wade across the river with his Pokémon just barely keeping the Carvanha at bay.
While all this is going on, Max, May, Brock, and the rest of their Pokémon hear an Aron down the beach. They go to inspect the noise and end up trapped in a cage by Team Rocket. Team Rocket only has a moment to be upset about Pikachu not being in the cage before they fall into their own trap. Taillow, the only one not to get trapped, takes a tape-recorded message to Ash. Ash, with Nurse Joy's help, hurries back just in time to send Corphish to free his friends before the tide comes in and immerses the cages in water. Team Rocket fails again at catching Pikachu and everyone happily thanks Corphish for its help.