May and Max take a moment to do some Pokémon spotting while the others prepare the camp. However, Max's enthusiasm keeps scaring the wild Pokémon off. May orders her brother to calm down, but Max explains that the real life experience is far more interesting than what he has read in books. Ash shares Max's sentiments, declaring that winning battles and making new friends is fantastic. The group suddenly finds themselves surrounded by a trio of hostile Mightyena. Ash takes a moment to check his Pokédex as May orders him to use some of his real life experience to combat the situation. So Ash sends Pikachu forward, and he is soon joined by Brock's Forretress and May's Torchic to even the match up. Pikachu is first to be struck down before a Poochyena comes running in, followed by Katrina. She explains that the area is a Pokémon Preserve. May replies that they are simply traveling through to reach Rustboro City. Katrina apologizes for her suspicions. As everyone introduces themselves, Brock cuts in with his overwhelming affection, causing Katrina to become uncomfortable, and the Mightyena promptly attack him. The scene cuts to Team Rocket, who have heard that the woods are supposed to be full of Pokémon, but haven't seen any. Then they notice one and suddenly they spot several more that they'd overlooked. Wobbuffet pops up, holding some kind of sign. Reading it, they see that it's a notice indicating that the area is a Pokémon Preserve. They immediately start plotting to steal Pokémon.
Katrina takes the group back to the Preserve Center, where she nurses sick Pokémon back to health. Brock claims that he, too, is a doctor, though Poochyena Tackles him to end the spiel. Katrina scolds it and Brock claims that she even scolds beautifully. Soon after, Poochyena is sleeping and Max takes the opportunity to scan it with the Pokédex. He declares that Poochyena must be ready to evolve, though Katrina doubts it, revealing that Poochyena is the same age as the group of Mightyena seen earlier. Katrina declares that it hasn't evolved yet, probably because it only uses Tackle. Katrina says that she is not worried - it's not a problem if it takes a long time to evolve or even if it never evolves. Max protests that Mightyena are much more powerful than Poochyena, and starts extolling the benefits of evolving to the Poochyena. May starts thinking about her Torchic evolving, and she learns from her Pokédex that Torchic evolves into Combusken. Max and May are instantly keen to have Torchic evolve soon, but Ash dashes their hopes of an instant result. He explains that Pokémon have to gain experience through battling first, and it takes a while. Max complains about why things take so long, and Brock offers him another perspective, admitting that if it were easy to evolve Pokémon, it would not be so fun. Ash elaborates that getting to know each other overtime is part of the experience. May queries why Pikachu hasn’t evolved, and Ash says there are different kinds of evolution. Brock proceeds with an impromptu lecture on evolution, demonstrating that many Pokémon like Pineco and Poochyena evolve with experience, while others such as Pikachu need an Evolution stone to evolve. He also touches on branched evolution, using Eevee as his example.
Max insists he wants to stay there awhile because Poochyena must be ready to evolve. Katrina says there's no guarantee Poochyena will evolve soon, but she does have room if they want to stay. Ash wants to hurry on his way to challenge the next Gym, but Brock immediately accepts in the hopes of getting closer to Katrina. Max tells Poochyena he'll do everything he can to help it evolve. Outside, Max gets Poochyena to battle Torchic, urging it to use Bite instead of Tackle. Torchic finally gets fed up and scorches both of them with an Ember before walking off. Max rushes back inside the cabin to ask Ash if he can borrow Pikachu or another of Ash's Pokémon to fight Poochyena. Ash seemingly agrees, but May enters the room and declares that Max will probably just get the Pokémon to lose deliberately so Poochyena can evolve. Ash says that such faked battles aren't good for Poochyena.
Later, Max is watching Poochyena fight one of the Mightyena, using Tackle over and over, and he becomes discouraged. Ash approaches him and says lots of Pokémon are happy the way they are and don't want to evolve, such as Pikachu. He asks if Max understands, and Max says he knows Ash doesn't want him to cheat, and unexpectedly calls Poochyena and runs off with it. Ash and May are left puzzled, but Katrina alerts them to something she found during one of her patrols; part of a trap for catching Pokémon. Ash and May realize there are Pokémon poachers in the forest. Meanwhile, Team Rocket proudly gaze at their pile of trapped Pokémon. They start fantasizing about a promotion and the benefits that will result, such as Jessie getting a new house. But Meowth interjects, alerting his teammates to Max, who is by himself as he wanders through the Preserve with Poochyena.
The Rocket trio quickly puts a plan into motion to fulfill Max's evolution ambitions. As Max starts looking for an easy target for Poochyena to attack, he spots a machine. Max tries to ignore it, but as he prepares to walk away, Jessie and James, disguised as scientists declare that they're doing top secret research and don't want Max to tell anyone about it. Max agrees, then asks what they're researching. James keeping up the ploy intentionally lets it slip that the machine is a part of their latest evolution research. Max is instantly intrigued, so Jessie offers him a free demonstration. She promptly places Meowth inside the machine, and with the hatch closed, Meowth emerges in a Persian costume. Max is fooled and very amazed, even asking for another demonstration. Team Rocket turns the "Persian" into a Sunflora, which really surprises Max, who protests that it's not possible for a Persian to evolve into a Sunflora. Jessie says that's what they told Albert Einstein before he invented the light bulb, to which Max says Thomas Edison invented the light bulb. James tries to keep up the ploy, but Meowth becomes confused by all of the quick changes and emerges in a Pokémon fusion costume. Jessie and James try to hide the mix up, but Max has become suspicious. As he prepares to walk away, Jessie snatches Poochyena and reassures Max that the machine will work. They drop Poochyena into the machine and the doors promptly slide shut. Jessie and James restrain Max by his arms as Meowth causes the evolution machine to explode.
Soon after, Team Rocket is thanking Max as they are about to leave with Poochyena and the other stolen Pokémon in their Meowth balloon. Max insists they give Poochyena back, and they refuse. Just then, Katrina, Ash and friends arrive on the scene. Katrina accuses Team Rocket of being the poachers and they proceed to unmask themselves and recite their motto and use a machine to grab Pikachu and start to float away. The three Mightyena lead the pursuit. Ash calls on Taillow's assistance. Taillow quickly reaches the balloon and begins Pecking the trio, forcing them to stop piloting their balloon which gradually floats towards the ground. Max urges Poochyena to Bite through the net in order to free itself and the other Pokémon. Poochyena is scared, but with enough encouragement, it does so. They all fall to the ground, Team Rocket looks dismayed and just then, Taillow's persistent Pecking causes James to loosen his hold on the Pikachu-grabber. With Pikachu now free, Ash orders a dose of Thunderbolt, which causes Team Rocket to blast off.
Max congratulates Poochyena on finally using Bite and saving the day. He says Ash is right. Poochyena's great whether he evolves or not. Poochyena comments happily before bursting into a bright white glow. Max and May are confused by the phenomena, but Katrina explains that it's beginning to evolve. The newly evolved Mightyena lets out a triumphant howl, Max is amazed, and the other three Mightyena come to congratulate their companion.