Ash and his friends arrive in Viridian City for the first time in a year, and they instantly make their way towards the Viridian City Gym. He resolves himself to defeat the Gym Leader and ascend to the prestigious Pokémon League. Suddenly, Gary arrives on the scene with his cheerleaders, mocking Ash. Gary reveals that he has already won 7 Gym Badges, and attempts to enter the Viridian Gym to fight its leader. Ash attempts to follow in after him, but the guards refuse, on the grounds that only one Trainer can enter the Gym at a time. After Misty's Togepi accidentally ends up inside a Fearow's mouth, Ash and his friends go in search of it. Meanwhile, Team Rocket is similarly searching for them.
Fearow drops Togepi onto the ground next to Team Rocket, as Jessie attempts to capture it. It manages to elude her, walking across a slim beam. Jessie follows after it, but falls to the ground as it cannot support her weight. However, her efforts are rewarded as Togepi lands in her hands. Giovanni accepts Gary's challenge for the Gym Badge, as Gary's Nidoking is pitted against his Golem. Nidoking manages to defeat Golem with a simple Tackle attack, as Giovanni sends out his Kingler. Gary follows suit, replacing Nidoking with his Arcanine. Similarly to how the previous battle went, his Arcanine is able to defeat Kingler without much difficulty. When Gary tells Giovanni that he should give up, Giovanni summons his third and most powerful Pokémon: Mewtwo.
Mewtwo manages to defeat Arcanine with its Psychic, sending it sprawling to the ground. Gary checks his Pokédex, which explains that there is no available data on it. Giovanni explains that he wants to test the full capabilities of his Pokémon's power, offering to Gary the use of as many Pokémon as he likes. Gary sends out Nidoking and Arcanine, both of which are levitated into the air and defeated. Giovanni tells him to give up now, as there is no chance of victory. Meanwhile, Team Rocket approaches Giovanni, presenting him with Togepi as a gift. However, he decries their incompetence, but is forced to leave the Gym in their hands after he is notified of an accident occurring.
Giovanni grants them use of three Pokémon to defend the Gym, as Team Rocket are ecstatic that they are now Gym Leaders. Meanwhile, Giovanni approaches Mewtwo, announcing that he has a new assignment for it. As Misty and the others search for Togepi, they hear its cry emanating from within the Viridian Gym walls. They force their way into the Gym, and Misty reunites with Togepi. Brock notices the incapacitated bodies of Gary and his cheerleaders, as Ash helps Gary up. Gary imparts information to Ash about the evil Pokémon that Giovanni possesses, and that no ordinary Pokémon Trainer can defeat it. They are interrupted by Team Rocket, who recite their motto, and reveal their status as the newly appointed Gym Leaders.
Ash does not believe Jessie at first, until she shows him the Earth Badge. He proclaims that he will defeat them in a Pokémon battle to receive the Earth Badge from them. Jessie releases a Machamp, a Kingler and a Rhydon, prompting Ash to release his Squirtle. However, Squirtle is defeated easily by Machamp's barrage of Karate Chop attacks. In response Ash is electrocuted from underneath, from which James explains that the Trainer will experience the same pain as the Pokémon if it is attacked. Ash releases his Bulbasaur, prompting Jessie to send out Kingler. Bulbasaur is attacked by Kingler, as he is electrocuted once more. However, Ash refuses to give up, despite Gary's pleas.
Ash regains his composure, using Pidgeotto's Quick Attack to ambush Rhydon. This causes Jessie to get a taste of her own medicine as she is electrocuted. Meowth attempts to end the competition by using an explosion device, but Gary knocks it out of his hands. Pushed into a corner, Jessie summons her Weezing and Arbok, resulting in Ash using his Pikachu's Thunderbolt to defeat all of Jessie's Pokémon. In turn she gets shocked, as Ash assumes victory over Team Rocket. Gary's cheerleaders support Ash, as Gary reluctantly acknowledges Ash's skills in battling. He grimly states that no-one, not even Ash, could possibly face the Pokémon he fought and win. Ash demands to get the Earth Badge from Jessie in recognition of his achievements, but she refuses.
Meowth notices Togepi playing with the explosion device, but before he can stop it from doing anything, both sides of the stadium blow up. Team Rocket blasts off again, and the Earth Badge falls into Ash's hands. As the Viridian Gym begins to collapse, Ash and Gary make their way out of the gym and into safety. Brock ponders what was the Pokémon that Gary fought, but Ash is too preoccupied with his full set of Gym badges to care. When asked as to the location of the Pokémon League, Ash replies that he doesn't know where it is. Brock suggests that they go to Professor Oak in Pallet Town to ask him about it. Ash agrees, and the three make their way back to Ash's hometown.
- Giovanni finally steps out of the shadows.
- One of Gary's Cheerleaders speaks out of unison with the others for the first time.
- The platforms Jessie and Ash battle on are exact replicas of the Pokémon League battle platforms.
- The "Who's that Pokémon?" in this episode is Mr. Mime.
- Ash won his Earth Badge more out of the stupidity of Team Rocket and less on the Gym battle itself.
- This marks the second building to be destroyed by Ash and Team Rocket in Vermilion City.
- "If I cried like that every time Ash lost I'd be waterlogged." －Misty
- "Maybe I could have just one more battle to test out my most powerful Pokémon. I'd like to test out this Pokémon of mine in battle. And go ahead, use more than one Pokémon if you're afraid of losing." －Giovanni