Ash and his friends arrive in Mossgreen Village, a village so small it doesn't have its own Pokémon Gym. Because of this, Ash feels that there's no reason to stop there. However, Brock reveals that their bag of Potions and Antidotes is empty, so they should stock up on supplies in town. Meanwhile, Team Rocket, hot on their trail, is about to make their move on Pikachu. Before they get far, however, they discover Meowth has a fever. Deciding that the loss of Meowth is worth the capture of Pikachu, Jessie and James begin to leave him behind. They are immediately scolded by a girl, who lashes out at them for abandoning their Pokémon, believing that Jessie and James were Meowth's Trainers. She then nurses Meowth back to health and, during this process, Meowth has fallen for the girl. She instructs Jessie to give Meowth medicine after each meal and skips off with her basket in hand.
In town, the group arrives at an herbal shop to purchase their medicine. Entering, they find an old woman grinding herbs. When they request to buy some Potions and Antidotes, she offers them a snakeroot that will cure insomnia and grow hair on their nose and tongue. The old woman is then scolded by the same girl who helped Meowth, her granddaughter, named Cassandra. Brock immediately falls for her, trying to make small talk about how he intends to be the best breeder, but Cassandra parlays the conversation into a Pokémon battle, which Ash accepts. At the battle, Cassandra sends out her Paras, while Pikachu leads off for Ash. However, before the battle, Pikachu tries to make friendly talk in a show of sportsmanship, but it causes Paras to cower in fear. Meanwhile, Team Rocket is spying on the battle, intent on stealing Pikachu; Meowth is distracted by Cassandra, as he intends to repay her for healing him.
Meanwhile, Cassandra admits her ulterior motive in battling: she wants to make this Paras evolve so that she can use Parasect's mushroom to help develop a miracle Pokémon medicine. Paras is acting cowardly, fearful of battling. Agreeing to throw the battle by going easy on Paras, the battle gets off to a rocky start when Pikachu fires a small "static bolt" at Paras, which unfortunately knocks it out. While Cassandra tries to get Paras back into shape, Misty suggests Ash try a different Pokémon. Ash's Pokédex reveals that Paras is both a Bug-type and a Grass-type, so he decides to send out Squirtle to give Paras the type advantage. However, Squirtle's weakened Water Gun also manages to knock it out. Desperate to help Paras evolve, Ash sends out Charmeleon, despite the massive advantage that he has, telling him to go easy on Paras. Charmeleon refuses to obey, gets too violent, and instead of doing an easy, soft attack, he launches a full-power Flamethrower at Paras before sending it flying by smacking it with his tail. This causes Paras to run away in tears. When Ash tries to rein in Charmeleon, he too is blasted in the face. Pikachu decides to hit Charmeleon with a Thunderbolt, enabling Ash to recall him. Ash can't believe Charmeleon is acting this way, as he was so excited when Charmander evolved, but apparently, he wasn't ready for it. Misty tells Ash to deal with Charmeleon later and focus on finding Paras.
As Paras is running away, it bumps into Meowth, who, wanting to help Cassandra, tries to get Jessie and James to help Paras. However, they want to know what's in it for them. Meowth then explains that if Paras evolves, Cassandra will be able to make her miracle Potion which would be worth millions. Meowth then explains that once they help Cassandra, she'll make Meowth the company mascot. Jessie and James don't see how this would benefit them, but then Meowth adds that he would make them his business managers as he'll probably have a lot of money to manage. Fueled by greed, Jessie and James agree, asking Meowth how they'll make their millions. Meowth then explains that he needs Arbok and Weezing as losing battles is their specialty. First, Arbok goes up against Paras, but before it can attack, Meowth intercepts and knocks Arbok down. Paras, believing it had defeated Arbok, is cheered by Jessie and James as if it had scored the knockout. This repeats itself with Weezing and with Meowth, causing Paras to get fired up.
Cassandra, with Ash and company in tow, manage to find Paras up a tree, and because of its visibly different mood, determine that it's raring to go. While Team Rocket is watching from a nearby bush, Ash sends out Pikachu to battle again. Paras goads Pikachu closer and manages to prod him in the tail. As Pikachu prepares to retaliate from the cheap shot, he is reminded by Ash to throw the fight, so instead Pikachu falls over, feigning unconsciousness. Ash then sends out Charmeleon for another chance, but once again Charmeleon starts to disobey. Ash can't understand this as it was always obedient before evolving. The old lady, Cassandra's grandmother, then explains that if the Pokémon's strength is greater than the Trainer's skill level, it won't respect them and take orders. Cassandra asks that Ash call back Charmeleon, but it breathes fire on him again before turning towards Paras, who finds itself cowering in fear again. Team Rocket then comes out of hiding and cheer Paras on to win, only to be burned by Charmeleon. Charmeleon advances towards Paras and is about to finish it off when Paras, in desperation, closes its eyes and throws out its pincer, which strikes Charmeleon in the stomach, causing him to collapse. Paras is surprised that it won. Soon after, Paras begins to evolve into Parasect. Everyone hails Parasect's success, including Team Rocket who are overjoyed. Charmeleon, however, recovers and angrily sends Team Rocket flying with a tail slam. He then turns back to Parasect for revenge. Cassandra attempts to protect it, but Parasect stops Charmeleon with its Spore attack, putting him to sleep and allowing Ash to recall him.
As Ash and his friends leave, they are thanked by Cassandra for their help. Ash is also reminded by Cassandra's grandmother that he'll never get control of Charmeleon if he doesn't improve his skill level. Brock even offers to be Cassandra's first customer for her miracle potion.
After the group leaves, Team Rocket drops in, and Meowth is nursed back to health once again. Cassandra is reluctant to let Meowth become the company mascot, not wanting to separate Meowth from the heroic Team Rocket, who she thanks for helping out her Paras. Meowth does not win the spot anyways, thanks to Cassandra's grandmother having just found a Persian in the backyard for the mascot role instead. As Team Rocket sulks off, their potential riches lost, Cassandra promises to treat the Persian like it was Meowth.