On their way to the Battle Arena, Ash and his friends are snagged by a net trap. But for once, it's not Team Rocket—it's a fellow named Mitch and his Loudred, and they're tyring to catch Jigglypuff! Mitch used to be a company executive until his daughter Lisa requested a Jigglypuff for her birthday, and for six months he's been in the woods trying to get one. Every Jigglypuff comes to tease him, and every day Jigglypuff gets away scot free. Plus, Lisa's birthday is tomorrow!
Ash decides to help Mitch out, but Jigglypuff puts everyone to sleep, even Team Rocket. What's more, it's tough, and it's not impressed when they try to lure it with food! So they trick it into battling Loudred and using Rollout, which rolls it right into the cabin—now covered in sound-reflecting panels. Pikachu battles Jigglypuff until it uses Sing, and the echoes of its attack put it to sleep.
Now Mitch can catch Jigglypuff, but he realizes it belongs in the forest after all. He and the kids return to town, where Lisa is happy to have her dad home even if he didn't bring a Jigglypuff. Just then, Jigglypuff comes flying in, angry at Mitch for leaving. It turns out that Jigglypuff liked playing with Mitch, and it decides to stick around. So now Lisa has two new Pokémon friends!
While traveling toward the Battle Arena, Ash and his friends are caught in a net and suspended in a tree. They first suspect that this is Team Rocket's doing, but Brock thinks it may be something else. A Loudred appears, followed by its Trainer, Mitch, who apologizes for the mix-up. After getting Ash and his friends down and bringing them inside his cabin, he gives them his business card, which describes him as a professional Pokéblock taster. An intrigued May checks out Mitch's Loudred on her Pokédex. Mitch makes it up to them by letting their Pokémon try some of his company's Pokéblock, which the Pokémon eat.
Ash asks Mitch why he left the company and who the trap was set for, which he hesitates to answer. Suddenly, the Pokémon—except for Munchlax, who is still eating—sense something coming from the bushes. A Jigglypuff emerges, and Mitch declares that he will handle it, ordering Loudred to use Mega Punch. The blow lands, but Jigglypuff bounces right back into action. Mitch calls for Hyper Voice, but Loudred is infatuated with Jigglypuff and unable to attack due to Jigglypuff's Cute Charm Ability. Jigglypuff giggles and unleashes a surprising Flamethrower, followed quickly by Sing, lulling everyone but Loudred to sleep. Jigglypuff laughs and escapes, prompting Loudred to snap out of its infatuation and wake Mitch up, who immediately expresses his anger over failing to capture Jigglypuff yet again.
High above in their balloon, Team Rocket notices Jigglypuff's skills and decides to catch it. Meowth fantasizes that Giovanni could use it as a decoration, exercise ball, and sleeping aid.
While the Pokémon are used as sentries around the cabin, Ash and his friends ask Mitch why he's out here. Mitch explains that he requested leave from his job six months ago to catch his daughter Lisa a Jigglypuff for her fifth birthday, which was her only request. He left home to go to the woods in which he knew that Jigglypuff lived. Being an amateur Trainer, Mitch at first simply tried throwing Poké Ball after Poké Ball at one particular Jigglypuff he had found, failing each time. Even after catching his Loudred, whose Soundproof Ability would be useful, the Jigglypuff has continued to outsmart him. Mitch reveals that Lisa's birthday is tomorrow, but he has already written to her saying that he would not be home for her birthday because he promised to get her a Jigglypuff. Ash and his friends agree to help Mitch capture Jigglypuff.
Team Rocket is listening in on their conversation using audio equipment while eating rice balls when Jigglypuff shows up next to them. They try to catch it, but Flamethrower makes them toast. They get back up to go after it, but Jigglypuff puts Jessie, James, Meowth, and Wobbuffet to sleep. Loudred and Mudkip alert Ash, his friends, and Mitch to the scene. Mitch and Ash challenge Jigglypuff to a battle using Loudred and Pikachu. Max warns Ash not to attack it directly and Brock suggests to Mitch that he use Uproar to render Sing ineffective. Uproar hits, but Jigglypuff hardly notices it. Pikachu uses Thunderbolt, but Jigglypuff jumps high into the air and hits Pikachu twice with Rollout. The third Rollout hits Team Rocket, waking them up and sending Meowth and Wobbuffet into Loudred's ears. Team Rocket recites their motto but gets interrupted by Mitch, who thinks that they are Ash's friends and hands them his business cards. Loudred blasts the two Pokémon out of its ears, hitting Jessie and James and sending them all blasting off. Jigglypuff escapes, but Brock suggests that outsmarting it might be better than battling it.
They set out a bowl of Brock's special Pokémon food as bait, but Jigglypuff does not care for it, to Brock's dismay. May tries to offer it Professor Oak's Pink Surprise Pokéblock, but Munchlax swipes it away in a flash. After thinking for a bit, Max figures out a plan to put Jigglypuff to sleep, making it easier to capture. As part of the plan, Mitch lures Jigglypuff into a battle. Loudred's Hyper Voice hits Jigglypuff, at which point Ash says that it can only escape now by using Rollout. Sure enough, it does and rolls straight toward Loudred, who dodges at the last second. Unable to stop itself, Jigglypuff rolls into the metal-clad cabin. Ash and Brock promptly shut the door behind it. Pikachu appears inside as well and uses Thunderbolt, which reflects many times but still misses. Jigglypuff uses Flamethrower, which also bounces around, hitting neither Pokémon. Jigglypuff bounces off the walls, dodging Thunderbolts until it slams into Pikachu. Both land on the floor, but Jigglypuff begins to Sing. Pikachu drifts off to sleep, but the metal also reflects the musical notes, sending Jigglypuff to sleep too. Ash awakens Pikachu and Brock urges Mitch that now is his chance. However, he realizes that Jigglypuff would be better off living freely in the forest and decides not to catch it. Mitch believes that Loudred would be a good enough present and the group leaves the woods. Jigglypuff wakes up later that night to a full bowl of Pokémon food but appears saddened.
The next morning, Mitch arrives at home and greets his wife on the front lawn. Lisa comes out as well, excited to see her father. Lisa is sad at first because she didn't get a Jigglypuff as promised, but is simply thrilled to have her father home again as well as Loudred to play with. From up above, Jigglypuff lands after having traveled while inflated to Mitch's house. It is angry that Mitch stopped chasing it in the woods, but Lisa is overjoyed to see it anyway. Mitch asks Jigglypuff if it would like to stay with his family, which it agrees to. Lisa asks Jigglypuff to Sing with her, but this results in them all falling asleep.