A peaceful day at Professor Oak's lab turns into chaos when a series of small incidents leads to a Tauros stampede! The mayor's son, Gilbert, is supposed to receive his first Pokémon, but the Tauros broke through the walls of the lab and now the starter Charmander, Squirtle, and Bulbasaur have all escaped. And when Gilbert does show up, he has a lot of attitude but very little affection for Pokémon: he just wants something cool and powerful, not a Kanto starter Pokémon! However, everyone's first priority is to catch the runaway Pokémon. Tracey and Ash's mom Delia will go one way, Professor Oak, Gilbert, and Ash's Bulbasaur head for the mountains.
In the forest, Tracey and Delia rescue Charmander from a stream. Up in the mountains, Gilbert is scared of the high, narrow path, and is ready to walk away even after he spots Squirtle stuck on a tree overhead. But when Gilbert falls off the path, Bulbasaur saves him—and when Professor Oak catches Squirtle but nearly falls off too, Bulbasaur makes another save. Then Bulbasaur plays with Squirtle to reassure it after its big scare. This gets Gilbert thinking about Bulbasaur's loyalty, and he even tries to play with Squirtle himself.
As for the missing Bulbasaur, it's been seen all over town. Now it's hiding in a tree, cornered by a bunch of wild Primeape! Gilbert is about to abandon Bulbasaur too, but Professor Oak tries to rescue it. When Gilbert sneezes, he tips off the Primeape to the rescue and they all attack! Gilbert and the little Bulbasaur wind up trapped by the Primeape at the edge of a cliff, but Ash's Bulbasaur jumps in to protect them. It hoists Gilbert and the little Bulbasaur to safety, and then scares off the Primeape.
Back at the lab, with everything back to normal, Gilbert decides the Kanto starter Pokémon aren't so bad after all. He decides to stick with the little Bulbasaur. He's learned a lot from the example set by Ash's Bulbasaur, and he even thanks it as he heads off on his own Pokémon journey!
At Professor Oak's lab, as Kingler watches some Marill do a dance, it gets dizzy and clamps its claw on Phanpy's tail. Phanpy then goes into a Rollout which sends Totodile up in the air. It lands near Snorlax, causing it to roll over and down a hill and in front of Cyndaquil. Cyndaquil runs until it falls off a cliff and uses a Flamethrower that awakens the Tauros and sends them on a stampede. Unaware of this, Professor Oak is working on the computer when Tracey comes in with some books. Tracey tells him that he still has to give the trio of first partner Pokémon a health check-up before the mayor's son arrives to start his journey. The Professor is surprised at this, so Tracey gives him some information to look over while he answers the door. Delia is at the door, and is welcomed by Tracey before he is smothered by Muk.
The three Pokémon have passed the health test so they are now ready for the mayor's son. However, they then hear a rumbling that turns out to be the Tauros stampede. They crash through the lab and Ash's Bulbasaur enters the hole made in the wall. Meanwhile, the trio of first partner Pokémon escape through the other hole. Before they can chase after them, the mayor's son suddenly appears inside the lab and comments on the hole. He then asks what Pokémon they have and says he would really like a Torchic but could settle for Treecko or Mudkip. He just doesn't want to get stuck with Bulbasaur, Charmander or Squirtle because everyone starts with them. Tracey tells Gilbert that it doesn't work like that and Professor Oak explains that it doesn't matter for the moment because they ran away. Gilbert laughs at this and then says he could settle for Pikachu since he remembers one kid who started with a Pikachu who has been pretty successful. Delia lights up and says that he is talking about Ash, though there were special circumstances that day. Gilbert says that he is special as well and that he isn't leaving without a Pikachu, although maybe he should start with Raichu since then he wouldn't have to worry about raising it. Tracey is really annoyed by this point and tells him that raising Pokémon is the whole point of becoming a Trainer. Professor Oak tells him to calm down and then explains that the runaway Pokémon need to be caught before something bad happens to them.
Outside, Professor Oak gives the runaway Pokémon's Poké Balls to Tracey, who then runs towards the river with Delia and Mr. Mime. Professor Oak tells Gilbert that they will search by the mountains, but then a woman calls him over with the new issue of Pokémon Monthly. He explains the situation and asks her to hold one for him and then asks her not to tell anyone. Gilbert tells Professor Oak that she will tell everyone, but the Professor doesn't think she will. All of Pallet Town, as it turns out. Through loudspeakers above the town, she offers a reward for information on the three runaways.
Tracey, Delia and Mimey have already located Charmander. It is by the river trying to touch the top of a Magikarp. If it falls in, its flame will go out and it will never be able to battle. It falls as it grabs onto the Magikarp and starts splashing around the surface of the water. Tracey jumps in and picks up the Charmander in time, but then slips on the way back across. Mimey lifts them up with Psychic and they reach the riverbank safely. Tracey returns Charmander to the Poké Ball.
Gilbert is now on a small ledge above a large ravine. However, Professor Oak assures him that there is plenty of room on the ledge and tells him to just not look down. Besides, he will be going to scarier and higher places on his journey. Gilbert says that he will have strong Pokémon to protect him then, which is why he doesn't want to start with anything weak. Professor Oak tells him that he doesn't have the right attitude and that maybe he should just go home. Gilbert agrees and starts to head back when they hear the sound of a Squirtle. It is hanging off a tree branch above them. Gilbert is worried but then remembers that he quit, so he turns around and walks off. But then he slips and falls. Luckily, Bulbasaur is there to grab him with its Vine Whip. Then Squirtle falls and is grabbed by Professor Oak.
Now on safer ground, they watch the shell with Squirtle inside. As Bulbasaur gently rubs it, Gilbert asks why they don't just put it back in the Poké Ball. Professor Oak explains that the Squirtle will be scared of the outside world, so Bulbasaur is just trying to make it feel more comfortable. Gilbert goes over to Squirtle and starts doing an impression of one of Professor Oak's classes. Squirtle comes out of its shell and jumps into Gilbert's arms.
Back in town, both groups report back. Bulbasaur is now the only one left and the earlier request for information has proved useful. The Bulbasaur has been traveling through town and is now being chased by a group of wild Mankey. As the Professor knows where they hang out, the group heads over there immediately.
The Mankey turn out to be Primeape, and they are surrounding a tree that the Bulbasaur is currently hiding in. Gilbert suggests that he can just take Ash's Bulbasaur since it is already at a high level and knows Vine Whip already. After he is told some sense, Professor Oak walks over to the Primeape and calmly assures them that he is just there to get the Bulbasaur. That doesn't work, but while he has their attention Mimey picks it up with Psychic. Suddenly, Gilbert sneezes, causing Mimey to drop the Bulbasaur right on top of a Primeape. All of the Primeape start to use Thrash as the young Bulbasaur runs over to the humans. The Primeape run towards them and they run away. The group run left but a Primeape jumps on top of Gilbert and he runs right. The Primeape run after Gilbert and the young Bulbasaur.
Gilbert soon reaches a gap too large to jump across and is now faced with that on one side and the Primeape gaining on him on the other. Gilbert realizes that he can't be afraid anymore and challenges the Primeape. This is brave but very stupid and luckily Ash's Bulbasaur arrives in time to use Vine Whip and send Gilbert and the young Bulbasaur over the gap. The Primeape start to attack Bulbasaur but it uses a Solar Beam that makes the Primeape run away.
Back at the lab, Gilbert is ready to leave on his journey with Bulbasaur by his side. Professor Oak tells him that he has come out of his shell and wishes him luck. Professor Oak, Tracey, Delia and Mimey wave but before Gilbert leaves he thanks Ash's Bulbasaur. As he walks off, the narrator tells us that while a good Trainer will catch many Pokémon, no bond is stronger than between a Trainer and their first partner Pokémon. They start their journey together and learn from each other and grow to be strong and powerful friends.