On their way to Lilypad Town and Dawn’s upcoming Pokémon Contest, our heroes are delighted to come across a beautiful berry orchard! It’s there that they meet Lulu, the daughter of the orchard owners, and her Marill, who Piplup falls head over heels for. But they also encounter what appears to be a bullying Elekid, who turns out to have a crush on Marill, as well! A rivalry flares up between Piplup and Elekid, as they vie for Marill’s affection. Team Rocket is also vying for something—stealing the “love triangle” of Piplup, Elekid AND Marill! In the process, Piplup and Elekid become allies. However, Team Rocket is sent blasting off again. Sadly for Piplup, Marill chooses Elekid, and as our heroes say goodbye, Piplup tries to be brave through the tears.
Then, Dawn informs her mom that she has sent her some rare berries as a gift. But when her mom reveals that she is going to be the Chairperson of the Twinleaf Festival, Dawn responds in a mysterious, shocked, and perhaps unhappy way about it...
The group come across a Berry orchard on their way to Lilypad Town. They see all kinds of Berries—including Tamato Berries, Oran Berries, and Grepa Berries. Piplup tries to smell a Berry only to get smacked in the head by a Marill. The others ask Piplup if he's okay and they see the Marill, which Dawn checks on her Pokédex. Piplup soon sees the Marill and falls in love. Dawn asks Piplup if something is wrong and Brock tells her that Piplup is in love.
Soon, Lulu runs in to find her Marill and the group. She introduces herself as and Dawn comments on the orchard. Lulu says that it is her family orchard and that her parents take care of it, however she is currently running it while they are away for three days. She invites the group to stay for the night admitting that she gets lonely all by herself. Brock and the others take up her offer, and then Lulu guides them on grand tour of the orchard. While admiring some hard-working Sunflora operating the water pumps, Piplup takes over the chore to impress Marill. Later, Piplup helps Marill with the watering, and Dawn cheers him on.
An Elekid soon arrives, narrowly missing Marill, while Piplup gets zapped. Elekid tries to hit Marill again, with Lulu telling the group that Elekid is a wild Pokémon who keeps coming back to the orchard. Marill hides behind Lulu as Piplup attempts to fend off the threat, only to be knocked down again. Ash orders Pikachu to assist, though Piplup is determined to handle the situation and pushes him aside. Piplup tries a Bubble Beam and Whirlpool, but is again struck down by Elekid’s attacks. Elekid mocks Piplup before leaping away. Brock then explains that as Elekid is an Electric-type Pokémon, it has an advantage against Piplup, who is a Water-type. Brock also explains that Elekid is attacking Marill, but none of his attacks hurt Marill, which could mean that Elekid has actually taken a liking to Marill, same as Piplup. Ash, disagreeing with the theory, counters that it was just that Elekid's attacks missed. The group then shifts their attention to a cluster of growing Lum Berries. Unbeknownst to the group, Team Rocket have been observing them from a nearby tree through binoculars, and decide to steal the Lum Berries, due to their ability to heal any status condition.
During the night watch, Lulu comes across a Sunflora wandering the orchard, however it actually a disguised Meowth scouting the area. Afterwards Lulu returns to the house, and with the lights all off, Team Rocket start Berry-pinching. However, both Piplup and Marill are having restless nights and rush outside to clear their heads when they spot Team Rocket. Marill lashes Meowth with an attack, destroying his Sunflora getup. Piplup prepares to send the trio blasting off with a Whirlpool, though Elekid is determined to be the hero and destroys the attack. A fights ensues between the rivals, with Marill leaping to stop it. After Meowth reveals that Piplup and Elekid are competing for Marill affections, Jessie nabs Marill with an extendable hand. The pair cannot attack as Jessie uses Marill as a shield, while James uses the opportunity to grab Piplup and Elekid in a loot sack. Following their very successful heist, Team Rocket immediately takes off in their Meowth balloon.
Later, Lulu and Dawn wake up to discover Piplup and Marill are missing. They scour the house and search outside, but find nothing. Lulu then shines her torch over the Lum Berry plants and realizes that they have been picked clean. Brock deduces that Lum Berry thief might be responsible for the missing Pokémon, so Ash calls on Staraptor and Gliscor for assistance.
Meanwhile, Piplup and Elekid continue to fight for Marill even while caged. Jessie is enjoying the drama, until the fight escalates and the colliding attacks blow Team Rocket's balloon up. Piplup, Elekid and Marill roll out of the crash site while the Rocket trio quickly recover and give chase. The next morning, Ash and the others come across the destroyed balloon, realizing Team Rocket was behind the heists. Elsewhere, Piplup and Elekid continue to vie for Marill’s attention, each showing off throughout the return journey.
Gliscor eventually locates Team Rocket, who have also just recaptured Marill, and alerts the group to the sighting nearby. Jessie and James call on Yanmega and Carnivine to lash Elekid and Piplup with Ancient Power and Bullet Seed. Piplup replies with a Whirlpool, while Elekid zaps Yanmega. As Elekid and Piplup high five each other, Yanmega knocks them down with another Ancient Power. Ash and his friends then arrive on the scene, so Team Rocket recites their motto. Dawn orders Piplup use Peck, leading Jessie to run backwards to evade his pointy beak. Yanmega flies in to defend her Trainer, though Elekid strikes back with an Electric attack. Ash calls out Grotle. Jessie orders Yanmega get up, however it is paralyzed. Jessie, luckily has a Lum Berry handy, however she eats it herself in a bid to cure Yanmega’s status condition. Her teammates scold her insolence. Ash lashes the trio with a Razor Leaf, and Jessie drops Marill as she tries to defend herself. James orders Carnivine retrieve Marill. Piplup steps up with a Bubble Beam, only to be knocked down by a Sonic Boom. Elekid, however, intervenes by zapping Carnivine before kicking Jessie away to rescue Marill. Grotle follows up with an Energy Ball which send Team Rocket blasting off.
Dawn checks on her Piplup, however he is heartbroken at the sight of Marill and Elekid getting along well. Later, everyone returns to the orchard. Lulu is grateful for the group's help and gives them a box of Berries as thanks. As the group sets off again, Brock offers Piplup some advice on love, though he still finds it hard to see Marill with Elekid. Later they arrive in a town, where Dawn contacts her mom via a videophone and informs her that a box of Berries is being delivered to her. Johanna is pleasantly surprised, and also reveals that she is scheduled to be the chairperson of the upcoming Twinleaf Festival.