The gang is coming closer to Petalburg City. They have lunch first and May and Max begin to imagine what will they eat when they get there. May grabs a sandwich, but a Pokémon takes it before she does. The Pokémon gulps others' food - it is a Gulpin. The gang hears a warning from the speakers - all residents must evacuate from their homes. After a while, no soul can be seen on the streets. A scream is heard - the gang goes inside, seeing that Gulpin eat a woman's bread. Ash's Pikachu comes to help, but the Gulpin overwhelm him. More Gulpin fall from the vents.
Officer Jenny arrives and her Tangela brings the gang and the woman outside. She brings them to the Pokémon Center where Nurse Joy sees the situation. An older man (which Jenny introduces them as Prof. Jacuzzi) says that once again the Gulpin population is rising. The Gulpin each year go to eat everything and Prof. Jacuzzi thinks they are headed for the center of town. Jacuzzi already has a plan to stop them, but the Gulpin go already. On the bridge, the gang, with Officer Jenny, wait for Gulpin as they arrive. Jacuzzi launches a rocket, revealing a giant PokéBlock for Gulpin.
The PokéBlock attracts Gulpin and Jacuzzi presses a button - the PokéBlock flies away, so do the Gulpin as well. However, Team Rocket takes the PokéBlock, saying it is theirs. However, Gulpin attack the balloon using Sludge to get them down. Next thing, they use Stockpile, blasting Team Rocket off and releasing the PokéBlock. Brock catches the PokéBlock, but Gulpin go after it, so Jenny releases Meganium, Tangela and Parasect. Tangela uses Vine whip, Meganum Razor Leaf and Parasect Stun Spore to hold the Gulpin off. Ash sends Treecko. Gulpin use Sludge, but Treecko evades and uses Bullet Seed, hurting the Gulpin.
Jacuzzi presses the button - the PokéBlock goes away (as the jet-pack is attached to it), so Gulpin leave to it. Team Rocket is hungry, but Jessie's Wobbuffet spots Gulpin leaving, so they will go to Gulpin in search for food. During the night, another signal is heard and the lights go off - an underground cable was cut, so Joy switches to a backup generator. The Gulpin are headed for the center again, with Team Rocket following them. Nurse Joy presses a button to seal the gates, forcing the Gulpin to go above ground. Gulpin go above ground, so Jenny sends her Pokémon to battle.
Officer Jenny's Pokémon and Ash's Pikachu attack, nevertheless more Gulpin head towards them. Professor Jacuzzi arrives and activates a machine, so Gulpin disappear in a purple light, Jacuzzi fires the Gulpin out of his vehicle. More and more Gulpin are absorbed to be fired away. One is left, but the machine stops working. The Gulpin is trying to go away, but Ash sends Treecko to battle it. Treecko uses Bullet Seed, but is negated with Gulpin's Sludge attack. Jacuzzi has enabled the machine to work, while Treecko uses Pond. At same time, Jacuzzi fires his cannon.
Inside the machine, Gulpin attacks, so the machines are broken. Jacuzzi attempts to repair, but the machine is destroyed. Two purple lights emerge - Gulpin and Treecko are free, but are huge! Gulpin's attack affected the machines, so the result is the gigantic size. Gulpin moves, so Treecko comes to stop it. People evacuate the area, while Treecko and Gulpin fight. Per Ash's order, Treecko throws Gulpin on the river. Team Rocket is seen going away with food they got, but when Gulpin flies over, it attacks, blasting them off. Gulpin uses Stockpile and attacks with Speedup, but Treecko dodges the attack.
As Treecko dodges, he shrinks down to his normal size. Ash calls it back, but Gulpin goes into the town again. May proposes to catching it, despite its size. Jacuzzi throws his Poké Ball, but Gulpin frees himself immediately. Nurse Joy gives him a Heavy Ball and Jacuzzi throws it. Moments pass on, but... Gulpin has been captured! Brock wonders if Gulpin would be still oversized, but Professor says that it shrinks to its own size. He sends it out, but soon calls it back when it is enormous. Nevertheless, Jacuzzi will still work on making it on its original size.
- Featured Pokémon: Larvitar, Treecko, Carvanha, Shedinja
- At the beginning of the episode, a classic Pokémon identification can be seen. In this episode, the Pokémon is Magmar.
- This is the last episode in which Officer Jenny is voiced by Lee Quick.