During Ash's battle against a Trainer, Pikachu is hit by the opponent's Beedrill's Twineedle. Pikachu retaliates with Thunderbolt, sending Beedrill to the ground. The boy orders Beedrill to get up, but it is knocked out. Brock announces that Ash and Pikachu win the battle. The boy thanks his Beedrill for doing a great job and shakes hands with Ash for the great battle. Afterwards, the group of four walk through the forest as they discuss the battle that just occurred. May and Brock remark that Ash and the Trainer shaking hands reveals true sportsmanship. However, Max criticizes the way Ash battled, commenting that he should have used Quick Attack to avoid Twineedle.
Suddenly, a Zigzagoon pops out of the grass and scurries away. Max is immediately excited and notes that the Zigzagoon appears larger than an average one. Brock suggests that it could be because of Zigzagoon's diet. Several more Zigzagoon appear, so Ash grabs out his Pokédex for more information. The other Zigzagoon appear to be interested in a nearby Sentret and Pinsir horde. Just then, an even larger Zigzagoon makes its presence known by speaking out and sounding very much like a human. It is then revealed that the giant Zigzagoon actually was a human when he takes off his Zigzagoon suit. The group of four exclaim in surprise. May freaks out, thinking that the Zigzagoon disguised itself as a human, and Max corrects her by saying that it actually was a human. May comments that she never knew that Zigzagoon could evolve into humans, leaving Max wondering if he and May are really related. As the Trainer prepares to challenge the Zigzagoon, May and Max approach him for a closer inspection. May is still doubtful and grabs the Trainer's face before she is finally convinced. Meanwhile, the Zigzagoon walks away. The Trainer yells at May and Max, claiming that it is their fault that he was unable to catch that Zigzagoon. His mood completely changes, however, when he discovers that they are wearing knickers.
Ash and Brock make their way over, and the group questions who this Trainer is. Instead of answering the question straightforwardly, the Trainer reveals a few of his Pokémon suits, including a Zigzagoon, Tentacruel, and Bellossom. He finally introduces himself as "Nicholai the knickerbocker", explaining that knickerbockers are Trainers that thrive on communing with nature while exposing their knees. He claims that May and Max are knickerbockers as well, and asks them to introduce themselves. Ash and Brock follow up by introducing themselves, as well, but Nicholai only seems to acknowledge May and Max, telling them that they have two very worthy names for knickerbockers. The two reject the idea of being called knickerbockers. Brock asks Nicholai why he was dressed in a Zigzagoon. Nicholai says that dressing up as a Pokémon allows him to become one with them and understand their inner feelings, making it easier for him to catch them. He says that he wants to catch a Zigzagoon before challenging the Petalburg Gym Leader. May and Max reveal that the Petalburg Gym Leader is their dad. Nicholai instantly asks them for a battle, and Max, being too young, offers up May as his opponent. When May tries to turn down the battle, Nicholai accuses her of being afraid to challenge him. She then accepts his challenge.
The group moves to a nearby field to battle, and Brock takes his position as the referee. Nicholai sends out his Mudkip and quickly changes into a Mudkip costume. May sends out her Torchic, and Nicholai notes that her choice of Pokémon is odd since her Fire-type is weak against his Water Pokémon. Ash declares that May can come up with a strategy, though Max has his doubts. Brocks announces that the battle has begun, and May tells Torchic to "start attacking" instead of calling out a move. Torchic's look of determination quickly turns into confusion, while May wonders why Torchic hasn't moved yet. Ash tells May that she has to tell Torchic what attack to use. May orders Torchic to use Ember, while Nicholai tells Mudkip to use Water Gun. Water Gun completely drenches the Ember, rendering it useless. May calls for a Peck attack and Max warns May not to let Torchic attack Mudkip straight-on. However, it is too late, as Mudkip blasts Torchic backward with a Water Gun, knocking it to the ground. May runs over and pleads Torchic to get up. However, Torchic is knocked out and Brock announces that Mudkip is the winner. Nicholai declares that it was easy to beat May, and is sure that getting a Badge at the Petalburg Gym will be just as easy. He leaves to go catch a Zigzagoon before challenging the Gym. Max is left furious, while Ash, Brock, and May shrug off the insult. While Nicholai is walking through the forest, Team Rocket spots him and his Mudkip. They then commence their plan to capture Mudkip.
At the same time, the group are also walking through the forest, as May laments losing her first-ever battle to Nicholai. Ash and Brock comfort May, stating that it was only her first match and that she was at a type disadvantage. May then realizes that Max is missing. Nearby, Max is seen spying on Nicholai who is on the hunt for a Zigzagoon. Nicholai throws a bunch of fruit into the surrounding bushes, and Max realizes that Nicholai is using the fruit to lure out the wild Zigzagoon. Meanwhile, Ash, May, and Brock are searching for Max, but to no avail. Ash decides to send out his Taillow to search for Max from the sky. Max has gathered a bunch of fruit in hopes that he will attract all of the Zigzagoon in the forest so that Nicholai won't be able to catch any. He calls out into the forest to get the Zigzagoon to come out. However, before he knows it, a large group of Zigzagoon have completely surrounded him. Nearby, Ash's Taillow has spotted Max, and the group run to catch up to him.
Max panics at the number of Zigzagoon surrounding him, and the Zigzagoon jump towards him to get the fruit. Ash and the group have finally caught up and hear Max's cry for help buried somewhere beneath the group of Zigzagoon eating the fruit. Ash commands Pikachu to use Thunderbolt which sends the Zigzagoon scurrying away. May rushes to her brother, but soon the Zigzagoon regroup and now surround the group of four. Ash is about to get Pikachu to use Thunder Shock, but Max says that all the Zigzagoon want are the fruit. Brock calmly offers the fruit to the Zigzagoon, but the one in front of him only kicks dirt in his face. May suggests that the Zigzagoon are so angry because they were interrupted just as they were about to eat. Just as the Zigzagoon continue closing in on the group, Nicholai in a Zigzagoon costume jumps into the center of the circle. Somehow in Zigzagoon language, Nicholai manages to get the Zigzagoon to follow him and he leads them to a tree that is growing the same fruit. Nicholai strikes a tree trunk to cause some fruit to fall to the ground. He has his Mudkip use Water Gun on the surrounding trees, which gets more of the fruit to fall down.
All the Zigzagoon are happily eating the fruit as Ash and his friends approach Nicholai to thank him. Max apologizes to Nicholai, while Nicholai apologizes back for speaking about his father in that way. Max then asks how Nicholai learned how to speak Zigzagoon. Nicholai says that words aren't needed to communicate; rather, what's important is to say what's in his heart. Nicholai picks a Zigzagoon to battle, and the Zigzagoon accepts. He quickly changes into his Mudkip costume and orders Mudkip to use Water Gun. The Zigzagoon avoids it and Tackles Mudkip. Eventually, Mudkip manages to land a Water Gun on Zigzagoon, and Nicholai throws a Poké Ball at it. He successfully captures it, but just as he is celebrating his new capture, something grabs his Mudkip. It turns out that it's Team Rocket in their balloon. Nicholai demands answers, and the trio proceeds with their motto. Ash orders Pikachu to use Thunderbolt, but Team Rocket deflects it back at them with a satellite. As they are about to drift away in their balloon, Nicholai refuses to let them leave with his Mudkip. He changes into an Aipom costume, using it to climb up a hill. The wild Zigzagoon see his efforts and begin digging into the ground in an effort to help. Nicholai changes into a Gligar costume and jumps off a cliff. He flies towards the balloon and snatches away the cage that Mudkip is in. Ash sends out his Taillow and orders it to use Peck which sends Team Rocket's balloon flying around before landing the trio in the pitfall trap that the wild Zigzagoon have dug up using Dig. As the trio emerges from the crash, they find themselves surrounded by Ash and the wild Zigzagoon. They climb out of the pitfall before Jessie and James call out Arbok and Weezing respectively. Arbok uses Poison Sting and Weezing follows with Sludge, but Pikachu dodges everything and hits back with Quick Attack. Finally, Pikachu sends Team Rocket flying with Thunder.
Ash's performance against Team Rocket impresses Nicholai, so the pair have their new Pokémon, Taillow versus Zigzagoon battle it out. As the two opponents struggle to think of attacks, Max admits that it is like watching the pair battle for the first time. The thrilling clash encourages May in her quest to learn to appreciate Pokémon.