Walking through a desert, Ash, Misty, and Brock arrive in Neon Town. In the city, a man bumps into Ash and is infuriated. Ash retorts, but Brock immediately advises Ash to apologize; Ash refuses to do so. Before the situation could escalate, Officer Jenny steps in, sending the man on his way, and tells Ash and his friends to find a hotel to sleep in. Misty notices that this Jenny is a bit edgy. Later, Team Rocket shows up in town and James bumps into the same man, who punches him repeatedly over the head. Meanwhile, Jessie is 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. Deciding to leave right away, they head to a forest outside the city and spot a Jigglypuff. Misty expresses her desire to catch one and 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. The gang then finds 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.
Hiding and spying on the gang, Team Rocket decides they want to use the Jigglypuff to put the people of Neon Town to sleep, in order to steal their Pokémon. They reveal themselves to the gang while wearing costumes and proceed to sing a tune radically different from their motto. After they finish, Team Rocket reveals their latest scheme. Ash sends out his Bulbasaur to battle; James sends out his Weezing. Bulbasaur's Vine Whip puts Weezing into a spin, resulting in Weezing's Poison Gas hitting Team Rocket instead. Misty calls her Staryu and orders it to blast Team Rocket away using Water Gun.
Afterwards, Misty gives Jigglypuff some lessons on breath control when singing. Pikachu sings as well, and when Ash compliments him, Jigglypuff gets annoyed and secretly kicks Pikachu. Before anyone can notice it, it hides behind Misty, who then inflates a balloon and puts it in Jigglypuff's mouth. The air inflates Jigglypuff and it goes flying. Brock also helps it by giving it a fruit that can help make its throat feel better. Jigglypuff takes a bite and instantly starts singing. Pikachu starts celebrating, but Jigglypuff kicks him again, and before the Pokémon can notice, Jigglypuff is already in Misty's arms.
Misty requests Jigglypuff to sing; it obliges and starts singing beautifully. Meanwhile, Team Rocket, hiding amongst some grass, sets up a tape reel recorder and a connected boom microphone to capture Jigglypuff's voice. As Jigglypuff sings, everyone falls asleep. When Jigglypuff notices everyone sleeping, it inflates itself in anger, 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 Double Slap. 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. Then, Misty decides to let Psyduck listen to Jigglypuff's singing, since Psyduck is apparently so dumb it wouldn't know if it was awake or asleep. After Jigglypuff sings for Psyduck, it still becomes angry, and Misty realizes that Psyduck fell asleep with its eyes still open. Meanwhile, Team Rocket finally wakes up and see their faces are covered with markings. They rub it off and proceed to check the recording. Unfortunately, the recorder did not capture Jigglypuff's singing and recorded their loud snoring instead.
Brock suggests they take Jigglypuff to perform for the sleepless people of Neon Town, which Team Rocket is happy to hear. When they get into town, the gang looks for a place for Jigglypuff to sing, to no avail. A stage truck then pulls over, driven by Jessie and James, disguised as rock stars, who offers them their stage. Once the stage is set, Jigglypuff starts singing into a microphone and begins to pull a crowd. However, its voice echoes throughout Neon Town's restaurants and gambling dens, causing everyone in the town to fall asleep. Team Rocket, whose ears were not plugged in properly, fall asleep as well. Once Jigglypuff is finished, it gets upset with its dormant audience and goes on to scribble markings on everyone's faces. The next morning, Ash and his friends wake up, only to realize what happened. Jigglypuff is nowhere to be seen, and they assume it must have left out of anger. When the townspeople wake up, they seem friendlier to one another; the man who bumped into Ash earlier even apologizes to him. Misty call outs for Jigglypuff, though there is no response. Team Rocket awakens and leaves the city looking very happy despite their latest failure.
As Ash, Misty, and Brock leave the city, unbeknownst to them, Jigglypuff follows close behind.