At the Eevee Evolution Lab, a female Eevee intensely watches her evolutions and tries to mimic some of them. First, she tries strutting like Sylveon, only to trip on a stone, before trying to swim like Vaporeon and nearly drowning in the process. Head of the Lab, Pinery, spots the Eevee and brings her into the lab to continue more experiments. She and her assistants try a Fire Stone first, but Eevee doesn't evolve as expected. The Thunder Stone also fails to trigger an evolution, leaving the scientists baffled.
On their way to school, Goh asks Chloe why she hasn't caught any Pokémon yet. Chloe replies that she has Yamper, though Goh remarks that Yamper actually belongs to her father and again presses for an answer. Chloe admits she probably won't catch any Pokémon, revealing that she wants to make her own decisions instead of feeling any pressure to follow in her father's footsteps as a researcher. Goh apologizes, and Chloe thanks him, adding that she will decide her own path in her own time. Chloe then wonders why Goh is attending school today, and he admits that he promised the teacher that he would attend school on any test days.
Arriving at school, the teacher orders Goh to leave any Pokémon in the school yard to play. As expected, Sobble is overwhelmed by its emotions and starts crying instantly at the thought of being left alone in the school yard with all the other Pokémon. Goh calls out his Cinderace to comfort Sobble, and it quickly finds the task to be daunting. Spying from the bushes, Team Rocket spots an opportunity to steal all of the students’ Pokémon and soon don school student disguises.
The Eevee wanders out of the Lab after spotting Yamper, who has abandoned Ash on one of his walks, going past. Eevee tries mimicking Yamper’s waddling walk and sneeze, leading her to be discovered. Yamper instantly becomes aggressive, and Eevee copies his intimidation attempt before trying to tackle Yamper, which fails miserably. Initially annoyed by the stranger, Yamper happily greets the Eevee with a wag of his tail. The lab assistants, armed with a net, chase after the Eevee, however Eevee and Yamper run away. Ash soon notices the pursuit, and is left confused when he sees Yamper and an Eevee being chased. The runaway duo reach the school gates, where Yamper quickly picks up Chloe’s scent and they escape into the school yard.
The familiar bark instantly gets Chloe's attention. Managing to excuse herself from the test, Chloe greets Yamper outside, wondering what he is doing at the school. Yamper beckons Chloe to follow him, and he leads her to the school rose garden to meet Eevee. Chloe is speechless and stares intensely at Eevee for several moments. Yamper interrupts the moment when he spots the lab assistants searching nearby. Chloe hushes Eevee before bundling her up to keep her safe, while the assistants walk past not noticing anything. Chloe soon gives Goh a call to meet her outside. Goh finds Chloe, Yamper and the Eevee hiding behind a hedge. He is quickly overcome with excitement at the sight of Eevee, revealing that Eevee has eight possible evolutions. Chloe admits she is hiding because it appears that some people are chasing after Eevee, and points to the suspicious lab assistants wandering nearby. Goh comes up with a plan, so he approaches the suspicious people directly while Chloe tries to escape undetected. His forthrightness leaves them both stunned, but the lab assistants soon spot Chloe carrying Eevee away. Goh resorts to tackling them, allowing Chloe to make a clean getaway.
Meanwhile, Team Rocket are vacuuming up all of the school students' Pokémon, including Goh's Sobble and Cinderace. While searching for Yamper, Ash arrives on the scene and orders them to stop. He and Pikachu fall into a pitfall trap, with Team Rocket gloating that they pre-empted the twerp's interventions. Soon, Goh and Chloe stumble upon the scheme, with the lab assistants closely behind. As the assistants order Eevee be returned, Goh and Chloe shout them down, adding that they will not hand Eevee over to "bad people" that want to hurt her. Realizing that two of them have mistaken them for villains, the lab assistants explain to Goh and Chloe that they're not who they think they are, but just researchers from the Eevee Evolution Lab, much to their surprise. Hearing Goh from a distance, Ash calls out for help and alerts him to the real situation at hand - the missing Pokémon. With a sneer, Team Rocket removes their disguises and performs their motto. Summoning the Rocket Prize Master for reinforcements, Meowth leaps into the coin slot to activate the device. Surprisingly, however, the vending machine doesn't work. James resorts to shaking it while Jessie shouts for Pelipper to take responsibility for the malfunction. Pelipper flies back immediately, and agrees to stand in for the battle against the twerps. Pelipper approaches with a Wing Attack, easily knocking Yamper back and not sustaining any damage from his Spark attack. Seeing Yamper get struck down, Eevee breaks out of Chloe's arms and decides it wants to battle as well. As Yamper begins charging up with electricity, Eevee uses Copycat to mimic it. James calls for a Hydro Pump next, while Eevee and Yamper launch a double Spark attack and send it blasting off. Team Rocket are shocked by Pelipper's quick defeat, but push forward with their scheme as they try to make off with the stolen Pokémon. Ash has Pikachu use Iron Tail to free the Pokémon from the net, followed by a Thunderbolt, which sends Team Rocket blasting off.
Eevee is later returned to Pinery and her assistants by evening, with Professor Cerise apologizing on behalf of Goh and Chloe's misunderstanding. Chloe is speechless as she watches Eevee leave with the researchers. The feelings seem mutual, as Eevee leaps from Pinery's arms and rushes to hug Chloe. Ash remarks that Eevee really loves Chloe, and Pinery agrees. She reveals that this Eevee is particularly mysterious, as she hasn't evolved during any of their experiments. Chloe clarifies that Eevee refuses to evolve into any of its eight evolutions, and Pinery admits that the genetics of any Eevee are unstable. She also theorizes that maybe this Eevee is hesitant to decide which evolution it undergoes. Pinery then asks Chloe to look after Eevee, and she happily accepts. Goh remarks that this will be Chloe's first catch and offers her a Poké Ball to make it official. Eevee leaps from Chloe's arms, wagging her tail in anticipation. Chloe then grabs the Ball, and crouches down before Eevee happily enters the Poké Ball. Chloe calls Eevee back out, and she enthusiastically leaps back into Chloe's embrace and quickly makes friends with the other Pokémon. Chloe also receives a pink Rotom Phone from her father, Professor Cerise, to commemorate her first step towards becoming a Trainer. Chloe scans Eevee with the Pokédex function, and considers Pinery's words about Eevee’s many possible evolutions. She then promises Eevee that they will take one step at a time, together.