Our heroes have stopped in a grassy meadow for a lunch break. Ash chokes on one of his sandwiches, Pikachu panics and zaps him which helps him swallow it. A friendly sheep-like Pokémon walks up to them and Brock says it's a Mareep, which have a mild disposition and can store electricity in their fleece.
The Mareep charges at them and jumps on Pikachu, who lets out a blast of electricity and the Mareep's coat gets fluffier. Then a whole bunch of Mareep appear and cluster around Pikachu as well. Poor Pikachu is frightened and zaps them, causing them all to fluff up.
A young girl comes running and tries to get the Mareep to back off but only her own Mareep listens to her. Then her mother comes along with a Raichu, whose Thunderbolt lures the Mareep away from Pikachu. The woman herds the Mareep back to their corral and tells the girl to return to the house. At their house, the woman apologizes for the trouble her daughter Mary caused. Mary says she only took her eyes off the Mareep for a second and they got away; her mother tells her she should be watching the Mareep and not dreaming about Pokémon battles. The mother explains that the Mareep in this valley have the best wool and every year there's a festival held in their honour with rides, shows and a Pokémon competition. Ash wants to enter but only people from the valley can enter. Mary wants to enter the competition this year but her mother says she's still too young.
Brock offers to help prepare the Mareep for the festival. They all go out to the meadow where Raichu and Pikachu round up the Mareep so they can be brushed. Team Rocket watches them, and plan to catch the Mareep to sell the wool and get rich. James reminisces about his boyhood, all his clothes had been made of Mareep wool. Jessie and Meowth get jealous. At sunset, Ash find Mary and her Mareep "Fluffy" practicing Thundershock on a target. He complements her and she says she has been training Fluffy since it was little. She asks Ash if she can battle Fluffy against Pikachu because she hasn't battled before, and Ash accepts. However, Mary gets ahead quickly by using Fluffy's Tackle and Growl attacks.
While Pikachu is disoriented from the Growl attack, Mary follows up with Speed Star and Thundershock. Pikachu counters with his own Thundershock, but Ash notices that Pikachu is getting worn out so tells him to stop using Thundershock and and dodge Fluffy's attack instead. Pressing her advantage, Mary tells Fluffy to turn up the power, but Fluffy collapses. Ash tells her that it used all its energy but would be fine after a good rest. Mary is upset, she had been so intent on winning she had forgotten about Fluffy. She thought that trainers had to be tough, but Ash tells her that it's not just attacks that are important, but a trainer also has to think about the condition of the Pokémon.
Later Mary's mother makes dinner for everyone and goes upstairs to call Mary, and she overhears Mary talking to Fluffy. Mary apologizes to Fluffy for making it battle too hard. She realizes that she's not ready to battle in the festival yet, and promises to think about Fluffy's feelings first. During the night a storm approaches. Mary's mom wakes everyone up and they take the Mareep out to a cliff. She explains that electrical storms charge up the Mareep and make their fleece look good for the festival. They take cover behind some rocks and watch as lightning strikes and the Mareep's coats get fluffed up and sparkling. Suddenly a net comes down and captures all the Mareep! Team Rocket hauls all the Mareep away with their balloon. Ash sends Pikachu but Pikachu gets captured by a robot arm. Mary's mother orders her Raichu to use Thunderbolt but the electricity is absorbed by a panel which causes the balloon to light up.
The Raichu tries harder and the panel is short-circuited, the balloon catches fire and crashes. The Mareep escape and catch Pikachu who's in a cage. The Raichu collapses, exhausted. TR sends out Arbok and Weezing, but Mary's mom tells the Mareep to stop them with a Growl attack. Then she orders them to Thundershock but Meowth uses the panel to reflect the electricity back.
Ash realizes that the Mareep need more power but he's having a hard time breaking Pikachu out of the cage. Fluffy jumps in front of the other Mareep, and Mary asks her mother to have all the Mareep concentrate their energy on Fluffy. Fluffy becomes supercharged and deals Team Rocket a major wallop. Ash finally breaks open the cage and Pikachu sends TR blasting off.
In the morning, Mary's mom gives her a PokeBall and says she's ready to use Fluffy in the festival. At the competition, everyone cheers from the stands as Mary releases Fluffy for her first battle.