Our heroes decide to take a break from their journey at a peaceful mountain steam. With everyone's Pokémon out, Misty tells her Poliwhirl not to drift too far away, when suddenly a Poliwrath comes from behind and bullies Poliwhirl around. The Poliwrath's trainer, Andreas, claims responsibility and begins to insult Misty's other Pokémon. Enraged, Misty challenges Andreas to a battle, but he declines, telling her he already has plans for today.
Continuing down the trail, the gang spots dozens of trainers with fishing rods all walking down the same path. Ash asks one of the fishers what's going on, and he tells him that the annual Seaking catching competition is on today. At a nearby lake, one of the officials announces the rules for the competition: Trainers can use any rods, reels, and lures of their choosing. However, the Seaking must be captured in a special Lake Ball, and only one Pokémon is allowed to accompany the trainer during the competition. At the end of the contest, the trainer with the heaviest Seaking will be declared the winner and receive a trophy as well as year's supply of chocolate bars. Ash notices the similarities to the Bug Catching Contest at the National Park, and with that in mind, he and Misty decide to enter.
Misty registers her Poliwhirl, and Ash registers Pikachu. The contest starts. Sitting in a secluded spot, Misty figures that getting a bite may take a while, when suddenly, Andreas already catches a Seaking not too far away. However, he lets the Seaking free, telling Misty he only catches small ones for practice. Someplace else, Team Rocket, not dressed in their usual uniforms, has entered the contest as well. Jessie uses her Jessie Lure, a lure that looks like a miniature version of herself. An hour later, with no luck, Meowth suggests that maybe the lure is scaring the fish away. Growing impatient, Jessie violently splashes her rod into the water. James restrains her, and she decides to use her Meowth Lure. Jessie then ties Meowth to the end of her rod and throws him underwater. Swimming around, Meowth spots a Seaking.
However, he unexpectedly gets caught on another rod, belonging to Misty. Both Jessie and Misty pull as hard as they can, and both their boats collide together. Not recognizing Team Rocket, Misty accepts Jessie's apology as they speed off. Andreas comes around and insults Misty again for still not catching any Seaking. Misty notices that the wind is changing direction, and decides to go to where the Seaking are going to swim. She spots Andreas heading in the same direction, and the two race.
However, Team Rocket's boat is in the middle of the path, and while Misty veers to the side, Andreas flies over their boat, creating a huge splash and capsizing them. Still not recognizing Team Rocket, Misty stops and apologizes for Andreas's actions. Ash finally gets a bite, and a giant Seaking leaps from the lake. Pikachu uses Thunderbolt, and Ash successfully captures it in his Lake Ball. At the same time, Andreas finds an even bigger Seaking. His Poliwrath uses Mega Punch and Double Slap, allowing the Seaking to be captured in his Lake Ball. The announcer declares that the contest will be over in ten minutes. With no Seaking yet and very little time left, Misty resorts to her secret weapon: The Super Misty Lure Version Four! The lure works, and a huge Seaking appears.
After having Poliwhirl attack it, Misty captures the Seaking with her Lake Ball. With the contest now over, the announcer declares that losers will receive a free commemorative badge. As James marvels over his badge, Jessie decides to steal the first prize trophy and the chocolate. Andreas's Seaking turns out to be 55 kilos. Just as he's about to claim victory, Misty runs up and has her Seaking weighed. It turns out to be 55 kilos as well. To break the tie, the official declares that the two must have a one-on-one Pokémon battle. Fighting in a battlefield very similar to the arena Ash fought Mandy at in the Indigo League, Misty uses Poliwhirl and Andreas sends out Poliwrath. Both Pokémon begin to exchange blows, when suddenly, Team Rocket appears from above and bags the chocolate. Poliwhirl and Poliwrath use Water Gun, and Meowth drops the chocolate. Ash sends out Bulbasaur to safely land the chocolate, then has Pikachu use Thunderbolt. Team Rocket's balloon explodes, and they're sent blasting off again.
Continuing the battle, Andreas commands Poliwrath to use Submission. Poliwhirl is beat up, and cowers behind Misty. She tells Poliwhirl to have more confidence, when Psyduck, Goldeen, and Staryu appear from their Pokéballs. Misty tells Poliwhirl that it has to keep on battling, because Andreas insulted all of its friends, and that if it tries its very best, it can never be called a wimp. Now determined to win, Poliwhirl decides to give it its best. Poliwhirl uses Bubble, followed by Mega Punch. Poliwrath shakes it off and returns the favor with Mega Punch, but Poliwhirl dodges, striking back with Bubble. Poliwhirl then uses Water Gun, and Poliwrath goes down. Misty wins the battle, and Andreas apologizes for his actions. Looking over her chocolate reward, Misty decides to split it amongst her friends and family, including her sisters, Brock's family, Tracey and Professor Oak, Ash's mom, Togepi, and Pikachu. Ash wonders about his own share, and as the gang talks it over, the episode ends.