Ash, Misty, and Brock jog along the road near the beach. A car races by Ash, and he gets disoriented by the exhaust fumes. He starts to cough, and walks into the path of another car. The car stops, fortunately, but it causes a massive traffic jam. Everyone starts to yell at each other, and Officer Jenny approaches on her motorcycle. She clears up the jam, and everyone continues on their way. Ash and his friends ask her why so many people are at the beach, and why they have surfboards, and she tells them that Humunga Dunga is coming. She explains that it's a huge wave that hits the island once every twenty years. They look at the ocean, and see several surfers trying to stick a flag or something into a large rock off shore a ways. Officer Jenny tells them that they're trying to be surfing legends, like Jan. She goes on to say that Jan was an excellent surfer who rode Humunga Dunga all the way to the top forty years ago. His flag can be seen flying at the very peak of the rock. Since then, everyone has been trying to match this feat, but no one has. Ash decides to try surfing out for himself, and dashes out to the ocean
. As Ash paddles out, Pikachu notices another, much older looking, Pikachu sitting on a cliff not far away. This Pikachu perks up, and looks out at the ocean, his tail starting to glow slightly. A man inside a cabin looks at him, saying "That's a big wave all right, but not THE big wave." Ash does pretty well surfing, but wipes out. Suddenly, his foot cramps up, and he starts to flail about in the water. A wave crashes into him, and he his knocked unconscious, face down in the water. Another, much larger wave approaches him, but the man on the cliff, with the Pikachu on the tip of his board, surfs by and scoops him up. He gives the Pikachu ("Pooka" as he calls him) different surfing commands and they go towards shore. Ash wakes up just enough to see the Pikachu sitting there, but drifts off again. Later, in the man's cabin, he wakes up. Brock tells Ash that the man's name is Victor, and Ash thanks him for saving his life. Victor looks out at Pooka, sitting on the cliff again, and tells Ash to thank him. Pikachu dashes out to Pooka, and joins him as he watches the sea. Team Rocket surfaces from the water in the Gyarados sub, and sees the two Pikachu sitting there. They prepare to steal both.
Back inside, Misty sings Togepi to sleep, and Ash and Brock talk with Victor. He tells them that he's had Pooka for twenty years, and remembers how he found him. He was floating on a piece of board in the ocean and landed right into his arms. They've been friends ever since. He says that Pooka is a mysterious Pokémon, for he can feel the waves in his body. He can sense when a big wave is coming and Victor tells them that they've ridden every big wave for twenty years. Misty notices some pictures on a wall. One is of Victor and Pooka twenty years ago, the other is of Victor forty years ago. Brock asks who the person is in the third picture with Victor, and he tells them that he's Jan, the surfer. He says that, when he was a kid, everyone wanted to be like Jan. In fact, Victor himself started surfing so he'd be like him. He'd try every day, and, through the support of Jan, he became better and better. He tells them that he thinks Jan could feel the waves within him as well, and always seemed to be waiting for something. One day, it came. It was the wave Humunga Dunga. He tells about how Jan rode the wave all the way to the top, and jabbed his flag into the peak of the mountain. He then says that, after getting to shore, he gave his board to Victor, telling him that he could do it too. He then set off in a boat to "surf the world."
He then tells them that, twenty years later, he challenged Humunga Dunga, but failed. After that, he got really discouraged, and didn't want to surf anymore. Then, he got Pooka, and everything changed. He says that he and Pooka have conquered every sort of wave together, and they're ready for Humunga Dunga. Ash tells him that he believes in him, and they hear Pikachu and Pooka cry out. They dash outside to see both in the clutches of the Gyarados sub's grabbers. Team Rocket appears, does their motto, and set off. They dive down, and Pikachu vainly tries to break through their glass cage. Suddenly, out of the depths, come several real Gyarados. James says that he's heard that Gyarados come to these waters every year to lay their eggs, and they hate to be disturbed. The Gyarados slam the sub a few times, and Team Rocket tries to leave. Unfortunately for them, the Gyarados aren't through with them yet, and Hyper Beam them out of the water. On the surface, Ash and his friends are in a motorboat searching for Team Rocket. The sub launches into the air and breaks apart. Pikachu and Pooka break out of their cage, and Team Rocket flies over the sea. Ash sends Bulbasaur out, and he catches Pikachu with his vines. Pooka falls to the water, and Victor throws out his surfboard, then dives into the water. The waves start to get rough, and Ash and his friends are forced to return to shore. As soon as Victor saves Pooka, Pooka starts to glow and bluish color. It's the big one, and it can be seen coming over the horizon.
On shore, Officer Jenny tells everyone to report to higher ground. Ash and his friends are worried about Victor and Pooka, as they can't see them. Suddenly, he notices them at the top of the wave, rapidly approaching the rock. Victor readies his flag, and the board flies over top of the rock. Victor jabs his flag into the rock, right next to Jan's, and everyone cheers. The wave crashes, and Victor looks out at what he did. Ash and his friends congratulate him, and he notices two kids standing among the crowd. "Hey, you could do it too," he tells them, and gives them his board. Ash and his friends smile.
Later that evening, somewhere out in the ocean, Team Rocket sits and waits as the Gyarados circle them. How are they going to get out of this one?