While Ash and friends are still discovering new islands, they come upon the seven Grapefruit Islands where groves of giant grapefruit are ripe and in season. When it looks like thieves are stealing the grapefruit, Ash, Tracey and Misty volunteer to help catch them. Surprisingly enough, what looked like hundreds of thieves was actually just one giant, hungry... and sleepy culprit!
Ash and his friends arrive at the Seven Grapefruit Islands, which are known for its large and bountiful grapefruit harvest. However, just as they pick a grapefruit for themselves, they are stopped by a girl named Ruby, who mistakes them for thieves. After clearing up the confusion, Ruby explains how they tend to the grapefruit trees to produce their high-quality grapefruits. However, Ruby also notes that they had been recently had a problem with thieves making off with the grapefruits. When the thieves strike again, Ash and his friends decide to go and help Ruby.
It is later revealed that the culprit is a Snorlax that has been eating the grapefruits. Devising a plan to stop Snorlax, Ash and his friends assist Ruby's staff in harvesting as many grapefruits as possible. However, all it does is lead Snorlax to their cache, and when Ash tries to fend off the Snorlax, Bulbasaur ends up being flattened by Snorlax's Body Slam.
Later, Snorlax has already eaten the first island dry. Thinking that they will be safe now that Snorlax has nowhere to go, they are surprised to find that Snorlax can swim, explaining how it arrived on the island. While Ruby and her crew try to pick the grapefruits as quickly as possible, Ash and his friends try to stop Snorlax. On the second island, Team Rocket is also picking grapefruits to steal. However, before they can make their getaway, Snorlax, followed by Ash and his friends, races towards them. Snorlax begins to eat Team Rocket's loot, which forces Team Rocket to team up with Ash's group to try to stop Snorlax. However, they are all are no match for it.
Thinking of alternative plans to stop Snorlax, they agree on trying to put it asleep. A massage by Ash's group does not appear effective, while James and Misty's methods make them fall asleep instead. Jessie gets an idea to use a Snorlax suit and pretend to be Snorlax's mother, but Team Rocket is sent blasting off from a Mega Kick. Now alone, Ash's group comes up with a plan to have Jigglypuffsing to it, though they need to find Jigglypuff first, and then, before anyone can fall asleep, catch it in a Poké Ball.
By chance, Ash and his friends find Ruby's staff asleep with their faces scribbled on. Surmising that Jigglypuff is nearby, they decide to build a stage for Jigglypuff, complete with colored markers and large signage. Just as Snorlax strips the second island and is heading towards them on the third, Jigglypuff shows up and begins to sing, while Ash and Pikachu manage to hold off sleeping long enough to land a Thunder on Snorlax and catch it in a Poké Ball. Once again, Jigglypuff uses its marker and the new colored markers to scribble on everyone's faces for falling asleep.
Later, as Ash and his friends leave the island, Ruby arrives to tell them that the islands stripped bare by Snorlax have since had new saplings growing. Ruby thanks them for their help by giving them a bag of candied grapefruit peels.
This episode has a rare instance of one Pokémon attempting to eat another.
When Jigglypuff is singing, it uses the actual microphone and the marker it carries around.
When Ruby is talking with the group about the grapefruit, Lapras seems to pass in the background twice. Either the production staff used the same clip from earlier and added on Tracey talking, or Lapras is moving around. However, when the group starts talking, Lapras is still floating around and not moving much.
After James's failed attempt to put Snorlax asleep, Tracey's fingers on his left hand seems to have been fused together.