Ash, Misty, and Brock are in Viridian City, and Misty lets Horsea out in a small fountain. Horsea, however, doesn't look to happy, and Brock suggests that Horsea needs some more exercise. Ash points out that they're no where near an ocean or lake. Brock wonders if there is an aquarium nearby, and Misty perks up, remembering the pool at the Cerulean Gym. Misty makes a quick call, and they all leave towards Cerulean City.
Upon reaching Misty's hometown, they see a poster outside the gym advertising an underwater ballet. Brock gawks at the picture of the star, and Ash notes that it looks a lot like Misty. Brock continues to stare at the picture, but follows Misty inside the gym, where they are greeted by her sisters. They scold Misty for taking so long to arrive, but she has no idea what she's talking about. Her sisters greet Ash and Brock, and Misty lets Horsea out into the pool. Her sisters run up, and tell her that they need to start rehearsing. Misty again has no idea what they're talking about, and they gesture over to a poster proclaiming the show. Misty asks if she could help out in some way, and Brock asks if the girl playing the mermaid had arrived. They tell her that she has already arrive, and he and Ash glance around, looking for her. Misty's sisters grab Ash and Brock's heads and point them at Misty. Misty is astounded, and refuses.
Misty's sisters tell Ash and his friends that no one has been coming to their performances anymore, and they came up with the idea of the underwater ballet. It was at this moment that Misty called, and they decided to have her star in it. Misty protests, but they go on, begging her to do it, telling her that the first show is the next day. Eventually, Misty gives in.
A bit later, they start the rehearsal. They tell her the basic plot, which involves two bad guys attacking the mermaid in order to get sunken treasure and a prince (Daisy) that saves the day. Seel, Ash, and Brock applaud, and they start. Outside, Team Rocket sees the poster outside the gym, and they think about attending. They realize that there will be a lot of water Pokémon there, and decide to steal them.
The next day, the stadium fills with people eager to see the show. Brock and Ash sit among the crowd, and soon the show begins. The pool rises out of the floor, and a spotlight shows several water Pokémon sitting about. Misty jumps in, and swims around with them. She swims into a tunnel, taking a breath in an air bubble there, and swims out among the cheers of the people. Lilly and Violet are watching from behind a curtain, and are approached by Team Rocket. They scream, and Team Rocket attacks them. Misty crawls into a large oyster, and the water Pokémon pretend to go to sleep. The narrator says that two villains appeared one day, and the spotlight turns on to show Team Rocket standing on the platform. Ash and Misty recognize them immediately, and know that they're up to no good. They jump up, and make their way backstage. Team Rocket jumps into the pool, and start to swim towards the water Pokémon. The oyster opens up, and Misty recognizes them as well. Team Rocket does their motto, and the crowd cheers, thinking it's all part of the show. Meowth pushes a button on a remote, and a balloon crashes through the ceiling.
Jessie and James toss a net out, and start to round up several Goldeen. Misty tries to stop them, but it isn't working. The narrator says that the prince came along, and Daisy is about to go out. Ash and Brock run up and stop her, then jump into the water with Daisy holding Togepi. Lilly and Violet fall out of a locker, and Daisy stares at them.
James notices Ash, Brock, and Pikachu swimming towards them, and Jessie sends out Arbok. Misty attacks Arbok with Horsea, who sends out a smokescreen. Arbok can't see, and a Seaking pokes him repeatedly with his horn. The crowd continues to cheer, all the while thinking that this is part of the show. James sends out Weezing, who turns out to be useless as he floats to the surface. Daisy sends out Psyduck, who is also useless, as he can't breath underwater. Ash sends out Squirtle and Misty sends out Starmie, and they help Seaking attack Arbok. Arbok is holding out pretty well, and is about to use a Poison Sting attack on all three when Seel intervenes, blocking the way. Seel swims circles around Arbok, and Headbutts him repeatedly. Daisy, Lilly, and Violet note how strong Seel is and regret never letting him be himself. Seel immobilizes Arbok with an Aurora Beam, and starts to spin and glow. Everyone wonders what's happening, and they watch as Seel evolves into the powerful Dewgong. Arbok tries to attack, but Dewgong whacks him with his tail, sending the snake hurtling towards Team Rocket. Dewgong freezes them up with an Ice Beam, everyone in the water climbs up onto a rock. Ash has Pikachu fill the pool with electricity, shocking Team Rocket, and making them fly out of the water. Dewgong hits them with his tail, and they fly out of the gym, hitting the balloon on their way out.
The crowd cheers loudly, and they all wave to the people. The next day, Daisy thanks Ash, Misty, and Brock for their help, as their shows are booked solid for six months. They ask to borrow some of Misty's Pokémon, and Brock suggests that she leave Horsea. They also ask for Starmie, and she grudgingly gives him up as well. Daisy picks Togepi up, but Misty yanks him out of her hands, offering Psyduck. They quickly turn him down, and pick up Pikachu. Ash yanks him away, and they all set off back to Viridian City, saying their farewells to Daisy, Lilly, and Violet.