On their way to Blackthorn City, Ash and his friends run into a female Trainer. Evidently, Brock fell in love with her, but he was not given much of a chance to display his affection, as the Trainer was eager to battle Ash. Using her Smoochum, nicknamed Josephine, against Ash's Pikachu, she begins the battle with a Sweet Kiss attack. Pikachu leaps over Josephine to avoid the smooches. Smoochum turns around and proceeds with the many Sweet Kisses. Ash urges Pikachu to wait for Josephine to come closer. Just as his opponent was approaching, Pikachu uses Agility and Josephine hits the ground. Pikachu follows up with after a Quick Attack from behind. Ash calls for the final attack, a Thunderbolt, but the Trainer cancels the battle and admits that she has had enough now. Ash pleads for another round, but she explains that she is too exhausted and recalls Josephine to her Poké Ball. The Trainer recommends that Ash should visit the Battle Park, a challenging facility operated by professional Trainers. She declares that the Battle Park has almost every Pokémon that exists, so the group decides to make a detour.
Meanwhile, Jessie, James, and Meowth are busy polishing Poké Balls at the said Battle Park, where they are working as employees. The Park warden supervisor suddenly enters the room and tells them that since the park is closed, it'd be a good time for them to clean it up, but first, he hands them another box full of Poké Balls. He laughs as they scream, and explains that he has the hard work and leaves to go shopping for supplies. Jessie furiously slams her fists onto the table. Meowth suggests that they should take the Poké Balls and leave, but James reminds them that they need the paycheck.
A familiar voice disturbs the trio's uproar, and they peek to see Ash and his friends waiting at the park gates. Brock shortly assumes that the Battle Park was closed, as there appears to be no workers or Trainers around. Just as they are about to leave, Jessie approaches and welcomes them to the park, and guides them through to the reception area, where James takes over. He offers them the opportunity to challenge the strongest Pokémon in the park with the Pokémon Pot Luck Grab Bag course. Ash is intrigued and promptly accepts James's recommendations. Jessie escorts the group through to the large entrance gates. The group wanders through the facility, but with no Trainers in sight until they are greeted by the Rocket trio posing as a mysterious trio of challenging opponents. Ash looks around for a Battle judge, and Brock voluntarily accepts the task.
James decides to be the first opponent, and he picks a Poké Ball from the basket, which turns out to be a Venusaur. Ash selects his Fire-type Cyndaquil to give him the advantage over Venusaur who is a Grass Pokémon. James starts off with a Razor Leaf attack, saying he was used to Grass-type moves from having a Victreebel. Cyndaquil dodges all the leaves, which instead slice through the surrounding trees. James continues with a Tackle attack, which knocks Cyndaquil into a tree. Venusaur now uses a Vine Whip attack, which Cyndaquil manages to dodge by jumping away, causing the vines to instead hit another tree which also falls. James tries another Vine Whip attack, which knocks Cyndaquil to the ground. Another powerful Razor Leaf attack is fired at Cyndaquil, but it escapes in a haze of Smokescreen. Cyndaquil takes control of the round with a Swift attack and follows it up with a Flamethrower. Venusaur stands up and uses a Solar Beam attack, which overpowers the Cyndaquil’s counter Flamethrower. The Solar Beam pushes Cyndaquil into a tree trunk, and this turns out to be the end for Cyndaquil. Ash is thrilled to have a challenging battle and is keen for another round of practice.
The second battle has now begun; while James and Meowth were arguing about who was to go next, Jessie sneaks in behind them and grabs a Poké Ball containing a Charizard, and Ash responds by choosing his Totodile. Jessie, used to fighting with her Arbok, orders a Poison Sting attack. As nothing happened, Ash lands a direct hit with Water Gun. After Jessie rejects the guidebook from Meowth, she orders the Charizard to use a Dig attack, which to everybody's surprise, it performs. Totodile narrowly avoids the follow-up Iron Tail attack. Charizard uses another Iron Tail, but Totodile dodges it and strikes back with a Headbutt attack. Ash orders a Scary Face attack, but Charizard uses an even scarier face. Jessie and Ash continue to up the stakes until both Totodile and Charizard collapse. Totodile gets up however and uses another Water Gun. After some thinking, Jessie commands the Charizard to fly up and dodge it, and use a Flamethrower attack. Ash responds to this by using yet another Water Gun, but it is overpowered by Charizard's intense Flamethrower. Totodile stands to its feet. Jessie uses another Flamethrower, but Totodile aims a Water Gun attack towards the ground, causing it to fly up behind Charizard. The maneuver gives Totodile the advantage, and it lands a Water Gun on Charizard, who crashes to the ground, ending the match.
As the third battle was about to start, James and Meowth once again argue, Jessie grabs the remaining Poké Ball and calls out a Blastoise, so Ash selects his Pikachu. Jessie chooses to battle by the book this time. While she was reading, Pikachu uses a Quick Attack. Jessie gets her act together and orders Blastoise to use a Skull Bash attack, which Pikachu manages to dodge. Jessie reads up on how to counter speed and commands Blastoise to use a Bubble attack. Nonetheless, Pikachu gets passed the suds and uses another Quick Attack. Ash decides to end this battle and Pikachu uses a Thunderbolt, but Blastoise Withdraws into its shell. A follow-up Hydro Pump attack blasts Pikachu into a tree. Blastoise uses another Hydro Pump, keeping Pikachu pinned to the tree. Ash is feeling the pressure now, and Pikachu's Thunderbolt fails to defeat Blastoise. Pikachu now uses a Thunder so strong that it causes the ground to split. Jessie rushes to Blastoise's aid, only to be hit by the electricity and crushed by Blastoise.
She quickly recalls Blastoise and sends out her own Arbok. Pikachu evades the Poison Sting, but he is nabbed by James and Meowth, who have since fetched the Rocket balloon. Jessie swiftly removes her disguise, revealing her true Team Rocket identity. James also reveals they had taken a sack of park Poké Balls as well. Out of nowhere, a park guard shows up, informing them that they cannot take those. As Team Rocket was about to escape, Ash calls out his Totodile, and Misty selects her Politoed. Ash and Misty both command their Pokémon to use a Water Gun attack, but only Totodile actually performs the move, which regardless breaks the steel arm holding Pikachu. Misty, upset with her Politoed as it continues to claps its hands together, orders it to use another Water Gun. This time, Politoed follows the command and blasts a giant hole in Team Rocket's balloon. As Ash, Misty, Brock, and the park warden approach Team Rocket's crashed balloon, the trio calls out the rental Venusaur, Charizard, and Blastoise. As Team Rocket basks in their power, the three Pokémon turn against them. The park warden proclaims that they are only obedient within the park. A combined Flamethrower, Hydro Pump, and Solar Beam hits Team Rocket and blasts them off.
The group continues their trek towards Blackthorn City by sunset. Misty admits that while Ash just battled against Team Rocket, the opportunity to go up against three very powerful Pokémon is invaluable. Ash agrees and declares that the practice has motivated him to win his final Badge.