While Ash and Serena do some special training and Clemont works on his inventions, Bonnie explores the forest, where she meets a trio of kids who call themselves the Lapras Defense Force. They show Bonnie to their hideout and introduce her to their friend Lapras, who is recovering from an injury and seems to be running a fever. The three of them really don't trust grown-ups, but when Ash, Serena, and Clemont come looking for Bonnie, the kids reluctantly agree to let Nurse Joy make a house call to their hideout.
After some medical attention, Lapras is feeling much better, but it keeps looking out toward the water and crying. Clemont figures out that it misses its ocean home, and the kids decide to take it back there. Despite a boulder blocking the way and a run-in with Team Rocket, Lapras is soon reunited with its family.
Bonnie bids farewell to her new friends, and our heroes resume their trek to Coumarine City!
After a lunch break, Ash gets stuck into training for his next Gym battle, Serena prepares for her Pokémon Showcase debut, and Clemont decides to start working on a new invention. Bonnie and Dedenne, meanwhile, decide to go take a walk in the forest and look for Pokémon.
Bonnie ventures into the forest until she is halted by three other kids named Heidi, Jay, and Kye. Bonnie demands to know why they won't let her pass, and they unintentionally mention that there is a Lapras in the forest by calling themselves the "Lapras Defense Force". The leader of the group, Heidi, offers Bonnie a place on the Lapras Defense Force if she can nuzzle Dedenne, which Bonnie allows. Dedenne zaps Heidi, however she makes a quick recovery which impresses the other kids. Then, a cry calls from far off, and the three bring Bonnie to their hideout towards the sound.
At a lake, Heidi orders the Lapras Defense Force to assemble, so they all change into swimsuits and prepare to swim towards their friend, Lapras. Bonnie asks Heidi how the group came across Lapras in the first place, and while Heidi is hesitant at first, she explains that the three of them had been walking a day after a storm, and after following some large tracks, had found an injured Lapras in the lake. Intending to treat and protect it, the three of them formed the Lapras Defense Force. After swimming more with Lapras, Bonnie wonders why Lapras ended up in the lake, and Heidi tells her that Pokémon poachers were most likely after Lapras. Heidi then ponders what would happen if 'grown-ups' became aware of Lapras, considering all adults 'grown-up liars'. Shortly after, the sky turns dark and rain begins to pour. Ash, Serena and Clemont return to the Pokémon Center to take shelter. Clemont expresses his worry that Bonnie had not yet returned from the forest.
Meanwhile, Bonnie and the three other children have sought shelter in a cave; the Defense Force's hideout. Heidi asks Jay for some candy, who always hides candy in his pocket. She takes it from Jay and offers it to Lapras as well as to the other children. Soon the rain clears, and while the children want to play, Lapras begins crying. Jay explains that Lapras had been sad in the past, though the children don't know why. Bonnie comes forward and touches Lapras, and notices that Lapras's skin is warmer than normal. Jay suggests that Lapras needs outside assistance, but Heidi retorts that adults should not be told. Then, Bonnie hears the voices of Ash and Clemont shouting for her from afar. She asks the other three children whether she could tell the others about Lapras as long as they weren't adults. Ash, Clemont, and Serena then arrive. Clemont comments that Lapras is really burning up, and should not be handled by them. He suggests bringing Nurse Joy, but Heidi again argues that adults cannot be trusted. She recalls a story of an abandoned Eevee the three had found and hidden behind the classroom. However, the three were caught by their teacher, who promised not to do anything as long as they told her what they were doing. But as soon as they did, the teacher took the Eevee away. Clemont and Ash insist that Lapras needs help now, and the three children start crying. At Bonnie's insistence, the three children agree to allow Nurse Joy to come.
Meanwhile, Team Rocket are arguing over a single croissant. Jessie suggests that the winner of rock, paper, scissors takes it all, only for Inkay to come out of its Poké Ball and eat the whole croissant. However, just then, Team Rocket see Ash running into the Pokémon Center shouting for Nurse Joy. The trio tail her and the twerps directly to the secret hideout and set their sights on capturing Lapras.
Sometime later at the Defense Force's hideout, Nurse Joy has finished treating Lapras and tells them that Lapras would be fine. Heidi, Jay, and Kye thank Nurse Joy, admitting some adults can be good, as Lapras happily dives back into the lake. Nurse Joy tells the three that the lost Eevee they had cared for in the past had been given back to its Trainer, making Heidi and the others realize their teacher wasn’t doing the wrong thing after all. Lapras then begins to cry sadly again. Clemont proposes that maybe Lapras wants to return back to the sea. Ash asks Lapras whether it misses its friends, and Lapras replies that it does. Ash then decides the bring Lapras back to the sea, but Heidi, Jay, and Kye argue that Lapras is their friend. Serena and Bonnie encourage them to return Lapras to its home and family, and the three children agree. Serena, using her Town Map, suggests following the river back to the sea. As they follow the river, a large boulder blocks Lapras's path. The group then call out Froakie, Hawlucha, Luxio, Chespin, and Fennekin, who easily break the boulder together.
As they continue along, Team Rocket interject, with James notably missing. Ash, Serena, and Clemont decide to take on Team Rocket while Bonnie and the Lapras Defense Force continue to take Lapras towards to the sea. However, as the Lapras Defense Force leave, Team Rocket fires off a smoke stream and flee in their Magikarp submarine. As the Lapras Defense Force continue towards the sea, they become blocked by James. Inkay uses Psybeam on Lapras, causing it to become confused. The other members of the Rocket trio join James, and then proceed to use claws from their submarine to grab Lapras. However, the Lapras Defense Force leap to help Lapras and begin fending off the claws. Heidi asks Jay for his candy, and feeds it to Lapras, which cures its confusion. With the four children on Lapras's back, Lapras then races towards the sea while dodging Team Rocket's attacks. Just as Lapras is about to be hit, Lapras's friends from far off block the attacks. The two Lapras then fire off an Ice Beam, freezing Team Rocket in ice.
Ash, Serena, and Clemont arrive, and Pikachu's Electro Ball blasts Team Rocket off. Lapras then leaves with its friends after farewelling the Lapras Defense Force. The next day, the group say goodbye to Heidi, Jay, and Kye and focus on the road to Coumarine City.