Our heroes trudge along, resigning themselves to the idea of camping out in the desert as the sun slowly sets. Suddenly they see bright lights in front of them: a glamorous city appears before them, covered in neon lights. They have found Neon Town, a city that is loud and boisterous 24 hours a day, famous for having no nights. The residents of Neon City sleep as little as possible and use all of their time to play. Behind the other side of the town's glorious facade, however, people are always angry and irritated. Fights being an everyday occurrence, Jenny, the policewoman, is terribly busy. Having had enough of a town so noisy one can't even sleep at night, our heroes head out into the peaceful forest. There they chance across Jigglypuff, the singing Pokémon.
Ash, Misty, and Brock are walking through a desert, looking for a place to sleep. By the time they arrive at a town by the name of Neon Town, it's already dark. In the city, a mean looking guy bumps into Ash and gets mad at the boy. Ash retorts, but Brock immediately advises Ash to apologize; Ash refuses to do so. Before the situation gets more heated, Officer Jenny steps in and stops them. Misty notices that this Jenny is a bit cranky.
Team Rocket shows up in town where James bumps into the same guy Ash had encountered earlier. He gets mad at the guy, but James ends up getting punched repeatedly over the head. Meanwhile, Jessie is getting spanked by a large woman for bumping into her.
The next morning, as Ash, Misty and Brock come out of a hotel, they notice several people arguing with one another; the group decides to leave the town and all of the chaos. They head to a forest outside the city and spot a Jigglypuff. Misty expresses her desire to catch one. She calls out Staryu, but Psyduck pops out instead. Misty scolds it and puts it back into the Poké Ball, much to her dismay. After that, she sends out Staryu and it uses Double-Edge on Jigglypuff. The little pink round Pokémon gets upset and cries. Brock finds this Jigglypuff strange. The gang then find out that this Jigglypuff has a problem with singing. Misty apologizes for attacking it earlier and hugs the Pokémon; she then decides that they should teach it to sing. Ash agrees.
Hiding and spying on the gang, Team Rocket decides they want to use the Jigglypuff to put the people of Neon Town to sleep. They reveal themselves to the gang wearing costumes and proceed to sing a tune radically different from their motto. After they finish, Ash sends out his Bulbasaur to battle; James sends out his Weezing. Bulbasaur, using its Vine Whip, spins Weezing around in circles, resulting in Weezing's Poison Gas attack to backfire on Team Rocket. Misty calls her Staryu and orders it to blast Team Rocket away using Water Gun.
After dealing with Team Rocket, Misty gives Jigglypuff some lessons on breath control when singing. Ash compliments her for having a good singing voice. Pikachu sings as well. When Ash compliments him, Jigglypuff gets annoyed and secretly kicks Pikachu. Misty inflates a balloon and puts it in Jigglypuff's mouth. The air inside inflates inside and Jigglypuff goes flying. Brock helps Jigglypuff by giving it a fruit that can help make its throat feel better. Jigglypuff takes a bite out of the fruit and starts singing. Pikachu starts celebrating, but Jigglypuff kicks him again, this time out of joy.
Misty requests for Jigglypuff to sing. Jigglypuff obliges and starts singing beautifully. Team Rocket, hiding behind some bushes, sets up the recorder to capture Jigglypuff's voice. As Jigglypuff sings, everyone falls asleep. When Jigglypuff notices everyone sleeping, it gets upset. It goes through Ash's backpack, pulls out a black marker, and scribbles markings all over their faces. It also finds Team Rocket sleeping and tries waking them up with DoubleSlap. Unable to wake them up, Jigglypuff scribbles on their faces as well.
Ash, Misty, and Brock wake up only to find their faces covered with markings. They rub it off and see that Jigglypuff is mad at them. Misty realizes that they must have fallen asleep during the performance and apologizes to Jigglypuff. Everyone tries to cheer it up by letting their Pokémon listen to its singing. However, all of their Pokémon also fall asleep, Misty gets an idea of letting Psyduck listen to it since Psyduck is so dumb it wouldn't know if it was awake or asleep. After Jigglypuff sings for Psyduck, Jigglypuff is still angry. Misty pokes Psyduck and it falls over revealing that it was asleep with its eyes open. Misty yelled at it for sleeping with its eyes open.
Team Rocket finally wakes up and see their faces are covered with markings, as well. They rub it off and proceed to check the recording. Unfortunately, the recorder did not capture Jigglypuff's singing; it recorded their loud snoring instead.
Brock suggests an idea of letting Jigglypuff perform for the people in Neon Town, which Team Rocket is happy to hear. When they get into town, the gang looks for a place for Jigglypuff to sing. A stage truck then pulls over; Jessie and James, disguised as rock stars, offer them their stage.
With the stage set, Jigglypuff starts singing. The voice is so strong that everyone in the town starts falling asleep. Team Rocket, whose ears were not closed properly, fall asleep as well. Jigglypuff gets really upset with all of them and goes to scribble markings on everyone's faces within the town. When the townspeople wake up, they seem friendlier to one another. The guy who bumped into Ash earlier even apologizes to him. Misty looks for Jigglypuff and realizes it was gone. Team Rocket awakens and leaves the city looking very happy, and in a good mood.
As Ash, Misty, and Brock leave the city, unbeknownst to them, Jigglypuff follows close behind.
In the dub's version of "Who's That Pokémon?", the Jigglypuff has green eyes, like it had been in one scene in the episode. Usually, only Shiny Jigglypuff have green eyes; at this point in time, Shiny Pokémon had not yet been implemented.
This is one of the few episodes in which Team Rocket does not blast off prior to the Best Wishes series.
The scene of Jessie getting spanked by the huge woman and James getting beat up was cut out of the Kids' WB! airing of the episode. However, it does appear in the Cartoon Network, streaming versions and the DVD/VHS version.