The episode begins with the group releasing their Pokémon and settling down to a meal prepared by Brock. Upon their release, Taillow, Torchic and Forretress are surprised to see Ash's newly caught Treecko. Nervous about the attention it is receiving, Treecko quickly climbs a tree and refuses to come down. The gang eventually return to their food, as do their Pokémon. From its perch, Treecko, spots a Seviper in the bushes.
Torchic gets over-excited and runs around with an apple on its head and a bunch of grapes in its mouth. Seviper trips Torchic up using its tail, causing Torchic to drop the grapes and the apple. Torchic runs off after the apple and stops in front of it. Torchic begins to dance happily, before noticing the huge snake Pokémon on the other side of the apple. Seviper eats the apple and Torchic gets angry. Seviper attacks Torchic and Treecko tries to save the tiny bird, but gets knocked back. Seviper hits Torchic around using its tail.
As the others rush up to help, Seviper uses its Haze attack so that they can't see what it's doing. Treecko sees that there is a gap at the top of the haze, so it jumps back up the tree again and sees Torchic being captive by Seviper's tail. It jumps down onto Seviper's head and Seviper drops Torchic. Treecko picks Torchic up and delivers it to May. Seviper gets furious and uses Poison Tail on Treecko, scoring a direct hit straight into a tree. As Seviper is about to hit Treecko again, Ash commands Taillow and Pikachu to use Wing Attack and Thunderbolt respectively, while Brock's Forretress uses Spikes.
After they get rid of Seviper, Ash and his friends run to Treecko, who's so weak it can't even stand up. They rush it to the nearest Pokémon Center, where Nurse Joy treats it.
Meanwhile, Team Rocket have been watching, and seeing the way Seviper almost effortlessly dispatched the Pokémon, decide they want to catch it. They see that it likes fruit, so they lure it with a basket of fruit left on the other side of a trap hole. Seviper just picks up the basket with its tail, stretches over the trapdoor, and glides away. Team Rocket get mad and jump out from the bushes, straight onto the trapdoor, and fall in. However, they don't let it discourage them. Turns out, they had a backup plan, but their plan using a net doesn't work either; Seviper just bites through the net.
Back at the Pokémon Center, Ash and Pikachu are observing Treecko. Meanwhile, the Rockets have lunch, during which they fight over the last rice ball. When they accidentally send it flying into the nearby brook, James and Meowth freak out, but Jessie calmly breaks out a rice ball she'd hidden "just in case", angering her partners. However, Seviper sneaks up on her and swipes the rice ball just seconds before she chomps down on it. Jessie gets mad and sends out Wobbuffet (The only Pokémon she has after releasing her Arbok) and commands it to "teach that thieving Seviper a lesson". Wobbuffet obeys, but as it can't attack until something or someone else attacks it first, nothing happens. James soon points this out after a moment, and a frustrated Jessie recalls Wobbuffet, grumbling about how it's "never useful when necessary". She then grabs Meowth and hurls him at Seviper, commanding a Double-Edge attack. As he soars towards Seviper, Meowth screams that he doesn't know that attack just before the Fang Snake Pokémon smacks him across the face with its tail, sending him flying backwards into his comrades.
As all three hit the ground, another rice ball is knocked out of Jessie's pocket and rolls towards Seviper. James and Meowth are surprised by this revelation as Jessie chases after the rice ball, though she fails to get it back. To the trio's horror, Jessie's hair gets caught in Seviper's jaws in the process and a large chunk of it gets cut off. Enraged, Jessie violently mauls Seviper mercilessly with her "Fury Swipes" and "Mega Kick" in front of her terrified partners, who are seen hugging each other in desperation and fear throughout the majority of the scene. The ferocious beating knocks Seviper out cold, and Jessie, still seething with anger even though she has calmed down a bit, seizes it by the neck. Fortunately for Seviper, James and Meowth quickly remind Jessie that she is supposed to catch it. This calms Jessie down, and, as James and Meowth sigh with relief, she tosses a Poké Ball at Seviper, catching it at last.
At the Pokémon Center, Brock is explaining Nurse Joy's position in the family to May (she's the younger sister of the second cousin of Nurse Joy in Oldale Town's first cousin) when Chansey rushes in and indicates that Treecko ran away from the Center. Ash and his friends run out, calling for it, and see it jumping down a waterfall, onto a rock, and into the water. They realize that it's training, trying to break the rock with its tail. After a few more jumps, Treecko has an idea. It spins to increase its power before hitting the rock, finally breaking it, much to the amazement of the group. Ash congratulates Treecko and runs out with Pikachu to meet it, but Pikachu gets captured by Team Rocket.
Ash, enraged, sends out his Taillow, while James sends out Cacnea against it, and yells as Cacnea hugs him, ordering it to use Pin Missile, to which Taillow dodges successfully. Jessie then sends out Seviper, and the "twerps" are surprised to see that it's the same one that faced them before. Treecko, after Ash's short speech, faces up to it, and after an exchange of attacks between Seviper's Poison Tail and Treecko's Quick Attack and uses its new spinning move, defeats it and rescues Pikachu. It says that now it's had its revenge, Pikachu can finish it off, so Pikachu uses Thunder to send the Rockets flying. Ash thanks Treecko for battling for him, and finds he's won Treecko's trust when Treecko turns and holds out its tail. Ash and Pikachu shake hands with Treecko's tail, laughing happily.