Team Rocket's latest Pikachu-snatching plan slips up, and Pikachu ends up lost in the woods. It's found by a friendly Turtwig who defends Pikachu from Team Rocket, but mistakes Ash for a foe as well! During this commotion, Ash and Pikachu are hit by Sleep Power from a nearby Oddish. Turtwig takes this opportunity to grab Pikachu and run off into the forest. Turtwig's friend Clara, a kind old lady, happens upon the scene and explains to our heroes that Turtwig is the leader of the local Pokémon. Looks like this time it's taking its responsibilities a little too seriously!
Ash finds Turtwig and explains that he and Pikachu are really best friends, though Turtwig doesn't believe a word of it until Pikachu confirms Ash's story. Now that everyone is on friendly terms, it's time for a lovely outdoor meal at Clara's lakeside home. However, nobody realizes that Team Rocket's Magikarp submarine is lurking in the water. The villains snatch Turtwig and Pikachu, but Ash and Piplup pursue them and Pikachu and Turtwig are soon free.
That's not enough to stop Team Rocket, of course. They come back for another kidnap attempt, only to be defeated by Pikachu. Ash and his friends then prepare to leave, but Turtwig wants to come along—after a battle with Ash, that is. Pikachu wins the match, which means Turtwig is now the newest member of the team!
Ash and his friends give chase as Team Rocket make a balloon getaway with Pikachu locked in a cage. Ash summons Starly to attack the rope holding Pikachu's cage. James sends out Carnivine, but it latches onto him as usual. Jessie kicks Carnivine, and the force pushes the balloon down, causing Starly to accidentally pop the balloon. The balloon crashes near a lake, surprising a nearby Turtwig, who finds Pikachu and opens up the cage. Carnivine attacks and Turtwig steps up to protect Pikachu. Turtwig immediately attacks Carnivine with a powerful Tackle, sending Team Rocket flying.
Ash and the others soon catch up to Pikachu, and Turtwig runs up to defend Pikachu, assuming that they are hostile. Dawn steps up to catch Turtwig by sending Piplup, attacking with Peck. Turtwig fires off a Razor Leaf, but Piplup ducks low to the ground and dodges behind a rock. The attack hits a nearby bush, injuring a wild Oddish who stumbles out and uses Sleep Powder near Pikachu. Ash rushes in to save Pikachu, though both take the attack, falling asleep. Turtwig quickly grabs Pikachu and runs off. Dawn and Brock attempt to pursue, but they run into an elderly woman named Clara. She takes them to her cabin and awakens Ash. She informs the others that Turtwig is a friend and a protector of the community. She recalled finding it in the area, feeding it and nursing it back to health, which prompted it to stick around. It quickly became a leader in the community.
Turtwig meanwhile gives Pikachu a piece of fruit. It breaks up a fight between a Geodude and a Mankey, giving both of them enough fruit to settle the matter. Ash heads out and finds Pikachu, and Turtwig quickly tackles Ash. Pikachu quickly tells Turtwig that Ash is friendly, and Turtwig quickly changes tone, ashamed at itself. Nearby, an injured Linoone appears. Dawn checks her Pokédex while Ash rushes to treat it. They take it back to Clara, where Brock treats it with herbs. Team Rocket surveys the group from their Magikarp submarine in the lake.
Brock cooks lunch for everyone, including the Pokémon. Linoone quickly finishes its food, and Turtwig gives Linoone its food portion. Ash applauds Turtwig, and Ash gives Turtwig another serving. Turtwig is so ecstatic that it quickly latches onto Ash's head in a manner similar to James's Carnivine, and Clara supports the fact that Turtwig is drawn to Ash. Clara has also experienced Turtwig's affection, but she manages to get Turtwig latched onto a stick instead of her head. Suddenly, Turtwig and Pikachu are captured in a glass capsule, pulling them back to Team Rocket's submarine. The trio quickly flees, so Ash jumps into the water after them, and Dawn sends out Piplup to help. Clara realizes that Team Rocket might be using the river to escape, so she and the others follow along the shore. Team Rocket notices Ash following and grabbing onto the capsule. They pedal faster to try and dislodge Ash, taking the capsule underwater. Turtwig tries to break the glass with Tackle, though Pikachu's Iron Tail and Thunderbolt breaks the capsule and also electrifies everyone around, both Team Rocket and Ash. Meanwhile, Clara stops running due to fatigue, but Ash and the Pokémon surface nearby. Turtwig is somewhat exhausted, though uses Synthesis to heal up. Meanwhile, Team Rocket surfaces and tries another attempt to capture Turtwig. They order Seviper and Carnivine to attack with Poison Tail and Bite, but Turtwig rushes up to attack Seviper with Tackle before using Bite to send Carnivine flying. As Carnivine and Seviper charge forward to attack, Pikachu uses Volt Tackle to send Team Rocket blasting off.
Everyone prepares to depart Clara's place, but Clara knows Turtwig wants to go. Turtwig rushes over and stops Ash, asking to go along, although it demands a battle. Ash obliges and sends Pikachu to face off against Turtwig. As Turtwig charges, Pikachu knocks it down with Quick Attack. Turtwig tries a Razor Leaf, but Pikachu dodges. Turtwig quickly follows up with Tackle, catching Pikachu off guard. Turtwig rushes forward again. Though Pikachu jumps up to dodge, so Turtwig bites onto Pikachu's tail, bringing him down. Pikachu tries to shake it off, but Turtwig is holding on tight. Ash orders Pikachu to use Iron Tail on a tree to remove Turtwig. It works, and Pikachu follows up with Thunderbolt, paralyzing Turtwig. Ash promptly throws a Poké Ball, and Turtwig goes inside. After a few moments, the Ball stops shaking, making the catch a success. With Ash acquiring Turtwig, they continue to Jubilife City.