Now that Ash has gotten the Volcano Badge, he and his friends need to get back to the mainland to get the Earth Badge in Viridian. They hurry towards the harbor, but crash into a Wartortle, missing the boat. The Wartortle is really upset over something, and Pikachu can't understand him. He has Squirtle come out, and he listens to Wartortle as he frantically speaks. Squirtle whips out his sunglasses and they both jump into the water. Ash and his friends quickly get into a boat, and follow them across the water.
After a few minutes of traveling, Ash and his friends see a small island rise up over the horizon. Brock looks at the map, and tells them that the island isn't labeled. Ash notes that the island looks a lot like a Squirtle shell, and they reach the shore. A few feet behind, however, Team Rocket is following in their Gyarados sub. Inside, Jessie peers through the periscope, while James and Meowth pedal, complaining that she isn't doing anything. Upon reaching land, Ash and his friends come across several Squirtle and Wartortle shells. Brock puts his ear to one, and tells them that the turtles are sleeping. Wartortle points over to a rock, and there sits a huge Blastoise shell. Ash dashes up, and hugs the shell. Suddenly, his eyes get droopy, and he falls asleep. Squirtle puts his ear to the shell, and immediately falls asleep as well. Brock and Misty look at each other, wondering what's going on.
A bit later, Brock and Misty are still trying to wake Ash up. Brock notes that this condition has to have something to do with the Blastoise shell, and Misty has Pikachu wake Ash up with a Thundershock. The shock not only wakes Ash up, but it also wakes up all the other Squirtle and Wartortle. Brock tells him what happened, and Ash says that when he put his ear up to the shell, he heard some sort of strange, familiar music. He asks the Squirtle and Wartortle if that was what they heard as well, and they all agree. Misty tells Ash that they should leave, but he refuses until they wake up Blastoise. They all agree to work together, and think of what to do. A little ways offshore, Team Rocket sit on their sub and wait for a good opportunity to capture Blastoise.
After a few minutes of translating, Brock gets the story down. The island is the kingdom for turtle Pokémon, and the Blastoise protects them all as their king. One day, Blastoise took a swim and never came back. They eventually found his shell floating in the water, and dragged him ashore. Upon doing this, all of them fell asleep. Another Wartortle, the one that Ash and his friends came across, saw them all like this, and swam to the mainland in search of help. Misty wonders aloud if this is the turtle Pokémon breeding ground, and Brock excitedly says that he could learn a lot of stuff as a breeder here. He dons a doctors outfit, and checks out Blastoise. Suddenly, the shell starts to wiggle, and a deep grunt comes from inside. Blastoise pops out, and the Squirtle and Wartortle are extremely relieved. His Hydro Pumps pop out of his shell, but one of them appears to be plugged up with some sort of pink thing. Squirtle jumps up and pokes at it, and an ear pops out. Brock and Misty think they know what it is, but Ash doesn't recognize it. They hear a strange song come from the thing, and they know exactly what it is: Jigglypuff. They all fall asleep due to the sweet singing.
Team Rocket, back at the sub, send Meowth out to the island to get Blastoise. He walks over, and falls asleep because of the song. Jessie reels him back in and try to wake him up, but he's out like a log. They decide to use the Gyarados grabber, which is a huge plunger attached to a rope. It flies out, attaches, and brings Blastoise back to the sub. Jessie and James congratulate each other and Meowth wakes up.
Back at the island, Ash wakes up and notices that Blastoise is gone. Everyone else wakes up, and the Squirtle and Wartortle frantically talk amongst themselves. Ash and his friends try in vain to calm them down, and Ash's Squirtle squirts them all. They all look at him, and listen to him as he talks. They start to chant with him, and Misty notes that Squirtle is a great leader. Ash tells her it's because of his training, but Brock thinks it may be just because of the sunglasses. Pikachu points to the trail the shell left, and they follow it to the shore. The Squirtle and Wartortle jump in and chase after the fleeing sub. Inside the sub, Jessie, James, and Meowth argue over who should get the credit for catching Blastoise. James kicks Meowth against the wall, which starts to leak. Jigglypuff, still inside Blastoise's pump starts to sing, and Team Rocket falls asleep as the sub starts to sink. The Squirtle and Wartortle show up and carry the sub back to the island.
A bit later, Ash and friends wake Team Rocket up, who jump up and start yelling at them. James tries to thank them, but Jessie whacks him and Ash expresses how he feels sorry for him. Team Rocket turns around and see all the Squirtle and Wartortle facing them. They quickly retreat into their sub, and it transforms into a type of tank that starts to chase the turtle Pokémon. They whack Ash's Squirtle out of the way, and continue to chase the other Pokémon. Ash and his friends try to wake Blastoise up, but to no avail. Squirtle and Pikachu combine their efforts, and succeed in two things: freeing Jigglypuff (who flies out and into the tank) and waking up Blastoise. The strong turtle grabs the tank, and prevents it from moving any farther. Team Rocket tries to grab him, but he snaps the grabbers in half. The Squirtle and Wartortle squirt at the tank, and Blastoise sends out two powerful jets of water, sending it flying into the air. Ash realizes that Jigglypuff is still inside the tank. Inside, he puts Team Rocket to sleep again.
The tank/sub falls into the water, and Ash's Squirtle swims done after it. They see an explosion, and soon afterwards Squirtle swims up to shore with Jigglypuff on his back. Jigglypuff starts to sing, and everyone falls asleep again. The angry Jigglypuff whips out his marker, and doodles on everyone. Later, after waking up, Ash and his friends set off, waving goodbye to the Pokémon. Meanwhile, Team Rocket drifts about on their sub, waiting to reach shore.