Pikachu and his friends arrive on the beach. As the others start playing on the beach, Pikachu says that they can play anytime on the beach. Suddenly, a Wynaut, looking weak and battered, wobbles from nowhere and faints in front of the gang.
When Wynaut wakes up, Pikachu asks what happened to him. In a flashback, a bunch of Wynaut, a couple of Pichu, and a Buizel were playing peacefully when Meowth, Cacnea, Mime Jr., Wobbuffet, Chatot, Hariyama, and Exploud appear; kick all of them out of the island; and claim it as Meowth's. Wynaut's story ends and Pikachu and his friends decide to help the Wynaut, Pichu, and Buizel reclaim the island. At first, the Pokémon were discouraged but Pikachu and his friends successfully boost their confidence. Pikachu decides to train the Pokémon first before battling Meowth and his goons.
The Pokémon tackled Corphish as their first training but none of them were successful. Eevee remarks that Corphish is overdoing it so he got an idea. When one of the Wynaut tackles him, he pretends to be beaten. When it was the smallest Wynaut's turn, he accidentally trips. Corphish chose Buizel to go next but he's too scared of doing it. Now, the scene shifts to Pikachu teaching the two Pichu Thunderbolt, then onto Squirtle and Marshtomp teaching the Wynaut how to dodge a Water Gun. Three of them made it, but the smallest one got hit. Lastly, Combusken teaches the Pokémon about countering attacks. Three Wynaut use Mirror Coat to counter Corphish's Bubble Beam and they succeed. Then, the smallest one tries, but his Mirror Coat wears off and he gets blasted by the Bubble Beam. He was send high above the ground, then crashes back. The training is now complete and the Pokémon are now ready for battle.
The gang uses a cable car, in which a boat is used as a cabin, to reach the island. Meanwhile, Meowth and Wobbuffet gazes at the view and Meowth daydreams about what he will do to the island. Suddenly, Chatot interrupts them and leads them near to the cable car. Meowth sees Pikachu and his friends and decides to confront them. Just as Cacnea is about to attack, Corphish cuts the rope holding Meowth's boat making them fall into the water.
When Pikachu and his friends reach the island, Hariyama and Exploud appears from nowhere and Meowth and his goons comes from behind. The gang then splits up. Several scenes show Pikachu and his friends winning. When they were gathered in a single spot, Meowth commanded Hariyama and Exploud to use their best moves (Hyper Beam and Solar Beam). It successfully deals great damage to Pikachu and his friends. Exploud then fires another Solar Beam at a Wynaut but was deflected back to Exploud by Wynaut's Mirror Coat. Then, Hariyama fires a Hyper Beam but the Wynaut used Mirror Coat to protect themselves. Meowth then commands both Hariyama and Exploud to attack them but the Wynaut counters the attacks and Hariyama and Exploud lands on one end of a seesaw. As a last ditch attempt, Meowth and his friends charge at Pikachu's gang, but the Pokémon send Meowth and his friends to the seesaw. Donphan sends them flying by landing on the other end of the seesaw and the Pokémon successfully reclaims the island.
Pikachu and the others are seen happily playing in the playground. Pikachu then discovers some watermelons and shares them with the others. The Pokémon play and ate watermelons all day. The last scene shows Pikachu and his friends eating watermelons and watching the sunset.