When May's Munchlax gets sick and there's no Pokémon Center nearby, it's a kindly old couple (and their Mime Jr.) to the rescue! They meet May and her friends and offer to help them out. James' Chimecho has gotten sick, too. But he sees a grand manor nearby and takes Chimecho there for help—it's the home of James' beloved Nanny and Pop-Pop, who looked after him when he was a boy. To protect their feelings, James lies about his line of work. And since Nanny and Pop-Pop are the ones who came to May's aid, he needs May and Ash to help cover for him when he finds out they're staying at the house as well!
With the help of Nanny and Pop-Pop, Munchlax is well on its way to recovery, but Chimecho is still sick. James is deeply concerned, not to mention very busy trying to keep Jessie and Meowth from eating all the food and stealing all the other Pokémon around the house! The last straw is when Jessie and Meowth try to creep away with Mime Jr. and Munchlax. James catches them and unexpectedly teams up with Ash to put a stop to their shenanigans... and keep Nanny and Pop-Pop from discovering what's really going on.
Soon Munchlax is ready to hit the road again, and May and her friends gratefully take their leave. But James is distressed because Chimecho is too weak to travel. He must leave Chimecho with Nanny and Pop-Pop until it fully recuperates, and both Trainer and Pokémon are sad to see each other go. However, Mime Jr. wants to travel with James, so he says his fond farewells and leaves with Jessie, Meowth, and his new Pokémon.
On the way to the Battle Arena, May's Munchlax falls ill, even refusing to eat. An elderly couple approach the group, and Ash and his friends are surprised to see the old man has a Mime Jr.. The woman says that Munchlax has a fever and needs help.
Meanwhile, James's Chimecho is also sick. James orders it to use Heal Bell on itself, but Chimecho is too weak to do so. He scoops Chimecho up and looks over the horizon for a Pokémon Center, but all he sees is a castle. However, this happens to be one of his family's vacation homes. He runs there with Jessie and Meowth in tow. He calls for the castle’s residents, Nanny and Pop-Pop, and they are very happy to see him. He explains that his Chimecho is sick, and James’s grandmother takes it in her arms. The couple looks back to see Jessie and Meowth, and they assume that Jessie is James's wife, and they congratulate him. James is shocked that they would think this, and he imagines what it would be like to be married to Jessie - doing chores while she orders him around. He freaks out and tells his grandparents that she is his executive secretary and Meowth is his manager. Jessie and Meowth take offense to this, and James takes them aside to explain to them that he doesn't want his grandparents to be disappointed in him for being a part of Team Rocket. James admits that the time with his Nanny and Pop-Pop was a break away from his extensive and busy study schedule. He was allowed to act as he pleased at the vacation home, and he loved how they took care of sick Pokémon. His teammates agree to stay quiet, adding that James now owes them.
The couple place Chimecho on a rest bed for it recovery from its extreme exhaustion. James looks on in concern, though instantly becomes distracted by the cuteness of Mime Jr.. James’s grandfather notices the “R” logo on James’s shirt, though Jessie covers for him, admitting that it is a company logo standing for “royalty” and “romance”. James worries that his parents are around, but his grandmother informs him that they're traveling the world, much to his relief. Suddenly, Ash's group walks in, and James is very surprised to see them. He runs outside and closes the doors behind him to talk to them, and they assume that he is there to steal Pokémon from "the nice old couple." He tells them the real situation, and tells them that he and his teammates won't do anything bad as long as they don't tell the old couple that he is in Team Rocket. Ash and the others agree to the truce.
Later, Munchlax is put on a bed next to Chimecho. Suddenly, everyone realizes that Jessie and Meowth are missing, so James runs around the house in a panic to find them, with Mime Jr. following. He finally finds them eating from the refrigerator, their faces stuffed with food. He yells at them, and the rest of the group shows up, so he tries to come up with an excuse to make it seem like nothing is wrong. Later, everyone walks around the home's giant greenhouse and looks at all the Pokémon living there. Jessie and Meowth split off and see an Oddish. Jessie stuffs it in the back of her shirt, but James knows that something is up. Oddish's leaves poke out of Jessie's shirt, so James pulls it out and lets it go.
At night, Mime Jr. walks in the giant room and sees James sitting over Chimecho, who is sleeping. It starts to run over, but May walks in the room from another door. James tells her that Munchlax will be okay, and that she shouldn't worry about it as he will stay there to look over both of them. She tells Munchlax goodnight, and then leaves. Mime Jr. then approaches James, and he asks if it came to keep him company. The answer is affirmative, and he tells Mime Jr. that it is very kind.
Meanwhile, Jessie and Meowth sneak through the house, planning to go back to the greenhouse to steal Pokémon. First, though, they sneak into the giant room, where James and Mime Jr. are sleeping. They take Mime Jr. and Munchlax, then head off and steal the Pokémon in the greenhouse. Ash wakes up and sees a light in the greenhouse. Then James wakes up and sees that Mime Jr. and Munchlax are gone, then sees the light coming from the greenhouse. Everyone finds Jessie and Meowth, who start to do their motto, with James doing his parts. Suddenly, he realizes what he is doing and tries to take the Pokémon back from them. The bag of Pokémon breaks open, and all the Pokémon flee, Mime Jr. running to James. Jessie sends out Seviper and Ash calls Phanpy to battle. James helps Ash by sending out Cacnea, and when Cacnea is about to attack Ash as usual, James orders it to attack Seviper. Cacnea complies, lashing Seviper with a Sandstorm and Needle Arm. Ash and James have Phanpy and Cacnea attack together, with the Hidden Power and Pin Missile combo sending Jessie, Meowth and Seviper blasting off. Nanny and Pop-Pop rush into the greenhouse having heard all of the commotion, and James admits they were simply playing with the Pokémon. Jessie and Meowth suddenly crash through the ceiling next to the couple and act like nothing happened.
The next morning, Ash's group sets off, May thanking the couple for the treatment Munchlax received. The woman wishes Ash luck at the Battle Arena.
Meanwhile, Jessie and Meowth wait in the balloon for James to arrive. James, however, is in the room with Chimecho, who is still sick. It wakes up, though his grandparents admit that Chimecho is too ill to be moved. James says he loves Chimecho, and remembers when they met and all the good times they had together. He realizes that he can't take it with him. Chimecho smiles at him and nods, letting him know it is okay to go. James starts tearing up while looking at his smiling yet sad Chimecho. James wipes away his tears and gets Chimecho's Poké Ball out of his pocket to give to his grandparents, but a couple of empty balls fall on the floor. Mime Jr. unexpectedly runs over and presses the capture mechanism on one, going inside the Ball. James asks why Mime Jr. wants to go with him, and his grandparents tells him that Mime Jr. has taken a liking to him. Chimecho smiles again. Team Rocket's balloon flies off, and the couple watch it go, revealing that James eventually told them he was in Team Rocket. They say that even though he is in the evil organization, they know they're grandson is still a kind person, and they hope that he does well in life. James looks back to the house, and sees through the window that Chimecho is sitting up, smiling at him. Tears streaming down his face, he waves goodbye to it, and the balloon flies off into the horizon.