Ash, Misty, and Brock are on their way towards Celadon City. Ash decides to call Professor Oak to show him the new badges he has earned. When Professor Oak answers the phone, Krabby is there with him. Ash shows Professor Oak his badges, only he is unimpressed. Professor Oak says Gary and the other two trainers that started on the same day as him have five badges. Ash gets mad when Professor Oak says that Gary has also caught 30 Pokémon. Professor Oak suggests to Ash that he catches more Pokémon to become a better trainer. Ash hangs up the phone, very upset.
Misty, Brock, and Pikachu are eating rice balls (or doughnuts as they call them) when Ash walks back to them. Misty and Pikachu notice that he is upset and they ask him what's wrong. Ash says he is very far behind compared to the other trainers and Brock tells him that Celadon City is about a day's walk from where they are at. Pikachu spots a Mankey close by. The Mankey hops over to Brock, wanting his rice ball. Brock gives it to him and Mankey climbs up onto a rock to eat it. Ash tries to catch it by throwing a Poké Ball at it, but Mankey throws the rice ball at the Poké Ball like Ash, which the Poké Ball captures. Mankey starts hopping around called Thrash. Mankey attacks Ash and grabs his hat and climbs on top of a tree with it. Close by, Team Rocket is trying to think of a way to catch Pikachu. Jessie has a plan, but Meowth says her plans never work. Jessie throws a ball of yarn at him to get him to stop talking.
Ash gets back up and sees Mankey on top of the tree with his hat. Ash runs to the tree and frantically tries to climb it. Misty says that its just a hat and Ash tells her he had to enter a postcard contest to win the hat. Misty remembers entering the contest and Ash said he had to send in a million postcard to win the hat. Ash gets up to Mankey in the tree, but Mankey jumps off of it. Team Rocket appears to steal Pikachu and Mankey curiously hops over to them. James kicks it away, but when Mankey was curious enough, it evolves into Primeape.
Team Rocket sends out their Pokémon to steal Pikachu. Primeape attacks Jessie and sends her flying into a rock. She tells Ekans and Koffing to attack Primeape instead. While Primeape is fighting Team Rocket, Ash's hat falls off of its head. Ash asks Pikachu to get it and tells Pikachu not to look Primeape in the eyes or it will start attacking Pikachu. Pikachu carefully walks over to pick up the hat, trying not to look Primeape in the eyes. But Pikachu soon does, and Primeape grabs the hat. Pikachu attacks it with Thundershock, but it only makes Primeape furious. Brock thinks Primeape is afraid of them and walks up to it. Primeape sends Brock flying into a rock. Primeape uses Thrash to chase after Ash and Misty with Team Rocket following them also. They split up, and Brock catches up with Misty.
Ash continues running, with Primeape smashing boulders in his path behind him. Meanwhile, Team Rocket puts a trap in Ash's path. Ash and Pikachu fall into the pit trap, Primeape stopping just in time. Koffing accidentally releases smog and Pikachu uses Thundershock. Ash climbs out of the hole, but Primeape is right in front of him. Ash remembers what Professor Oak said and gets serious about catching Primeape. He first sends out Squirtle to use Water Gun, but it does nothing. Ash then sends out Bulbasaur to use Razor Leaf, but Primeape punches the leaves. Ash then sends out Charmander and it uses Flamethrower. Primeape dodges it and punches Charmander. Charmander then learns Rage, giving Charmander more power. Pikachu quickly grabs Ash's hat off Primeape's head and Charmander uses Flamethrower, knocking Primeape out. Ash throws a Poké Ball and it shakes, then it stops. Ash has officially caught Primeape!
Pikachu gives Ash his hat back just as Team Rocket climbs out of the hole. They wonder where Primeape is and Ash sends out Primeape and it starts attacking Team Rocket again, sending them flying. Primeape knocking Ash then he recalls his Pokémon and Brock says that they have reached Celadon City. Misty says that Primeape chasing them made them get here quicker. Team Rocket lands in a field full of serious Primeape. The Primapes start attacked Team Rocket and Meowth wishes he had rice balls.
- Ash captures a Primeape.
- Ash and his friends reach Celadon City.
- The other three trainers who left Pallet Town on the same day as Ash have already passed through Celadon City and earned their fifth badge.
- According to Ash, he sent in "about a million postcards" to win his official Pokémon League Cap. Misty entered the same competition but only sent in one entry, thus not receiving the cap.
- This episode's dub title is a reference to the Disney movie Herbie Goes Bananas.
- In Mystery at the Lighthouse, Professor Oak tells Ash that Gary has caught forty-five Pokémon. However, in this episode, Professor Oak tells Ash that Gary has caught thirty Pokémon. It should be noted that this was also present in the Japanese version.
- The writing on the Poké Ball in the advertisement is spelled "POCKEMON LEAG".
- The "doughnut" is actually a rice ball in the original Japanese version.
- The scene where ash demands his hat back is used as a joke in the Team Fortress 2 community since team fortress 2 is made fun of by having more hats in the game then weapons.
- The "Who's that Pokémon?" in this episode is Primeape.
- Ash: "It's a doughnut!"
Misty: "A Doughnut Pokémon?"
- Misty: "I didn't know that was an official expo hat. I remember entering the same contest myself."
Ash: "I had to send in a million postcards to win that hat!"
Misty: "He he. No wonder I didn't win, I only sent in one."
Watch this and other episodes: Pokémon Episode 25: Primeape Goes Bananas