The kids have stopped by the Banana Slakoth Garden on their way to Lilycove City, but the gate is closed and the trees have no fruit on them. When they meet the director, a man named Marcel, they find out a Snorlax came down from the mountains looking for food and has been eating all of the bananas.
Ash decides the only way to take care of Snorlax is to catch it, so he and Pikachu confront the giant Pokemon just after it eats. Unfortunately, Pikachu's attacks have no effect and Snorlax puts them all to sleep with its Yawn attack.
After consulting with Professor Oak, they get the recipe for a PokeBlock that will feed the ravenous Normal-type and he advises them to use a Pokemon that can't be put to sleep to catch it. Slakoth's evolved form, Vigoroth, is one such Pokemon.
Marcel talks to all of the Slakoth, trying to convince them to help save their home and one comes forward. They have it battle and defeat all of Ash's Pokemon, gaining enough experience to evolve into a Vigoroth. The next time, the Snorlax wakes up, Marcel and Vigoroth challenge it to a battle.
When Snorlax's Yawn attack proves ineffective, it uses Hyper Beam instead. Vigoroth attacks furiously, eventually knocking down the giant Pokemon with Focus Punch.
The park reopens, the Slakoth are happy and Marcel shows the kids what he did with the Snorlax--placed it in the center of a relaxation chamber where people can take a refreshing nap.