Ash's training battles with Dawn catch the eye of Theresa, a young woman with a strange request: can she borrow Pikachu for three days? Theresa and her aunt Abigail run a cake shop, but Abigail's Pikachu, Sugar, has disappeared and Abigail will surely need Sugar's help to win an upcoming baking contest. Ash agrees and the gang goes to Theresa's home, pretending that Pikachu is Sugar.
Abigail takes Pikachu into the forest, where it uses Thunderbolt to zap berries and give them a delicious roasted flavor. Team Rocket notices this unusual electrical activity and tries to seize Pikachu, but Abigail and Pikachu defeat them with ease. Abigail then challenges Ash to a friendly training battle, her "Sugar" against Ash's Aipom, only to cut the battle mysteriously short after just a few rounds.
That night, Ash feels so guilty about deceiving Abigail that he confesses the entire plan. Abigail reassures him that she knows Pikachu isn't Sugar, and Sugar really left because it was unable to crack open Aspear Berries for her. The moment is spoiled when Team Rocket nabs Pikachu, but a Raichu springs out of the woods and comes to the rescue. That's Sugar, who learned Focus Punch to crack open the Aspear Berries and even evolved into Raichu. Abigail's sure to win her contest and now our heroes are confident that they'll win their competitions as well!
Ash and Dawn are having a practice battle with Pikachu and Piplup in order to prepare for the Floaroma Contest. Pikachu attempts an Iron Tail but Piplup dodges and uses Bubble Beam. Pikachu executes several backflips to dodge. Dawn switches Piplup out for Pachirisu. Pachirisu uses Discharge but Pikachu absorbs the attack with his tail. Pikachu fires Thunderbolt but Pachirisu dodges. The attack destroys the rock it was on and causes a dust storm. When it clears, a woman marches up to Pikachu and asks to borrow Pikachu for three days. She introduces herself as Theresa and Brock immediately goes for her, but Croagunk stops him.
The group head to a bakery where her aunt (grandmother in the original Japanese version) Abigail bakes cakes, but since her Pikachu, named Sugar, disappeared, she's been down. Theresa wants Ash's Pikachu to pretend to be Sugar in order to help her win a cookoff in three days. Ash mentions that she might be able to tell that Pikachu isn't the same, but Theresa mentions that Sugar would scratch its head with its tail occasionally. Pikachu mimics the move, with Theresa approving, saying that it's just like how Sugar does it. Ash agrees and they head to the bakery. Pikachu marches up to Abigail and scratches his head, passing the act. Guests come by and greet "Sugar", the façade working perfectly as Ash and his friends watch, noticing Abigail's better mode. Abigail grabs a basket and heads out with Pikachu. Theresa mentions that she is going to get Berries for the ingredients.
Meanwhile, Team Rocket walks along with several boxes of Berries when they notice a powerful Electric-type attack. They decide to head over, finding Pikachu using Thunderbolt to dislodge Aspear Berries from a tree. Abigail gathers them as Team Rocket watches, noticing that Pikachu is Ash's and deciding to poach it. Back at the bakery, Ash and his friends listen to Theresa talking about how Pikachu's Thunderbolt helps in baking. Ash decides to find Pikachu to make sure his Pokémon is doing okay. Abigail gathers the basket of Berries as Team Rocket confronts them. Team Rocket recites their motto. Pikachu prepares to attack as Ash and his friends notice. Ash wants to help, but Theresa holds him back. Theresa confronts them as Jessie's Seviper attacks Pikachu. Abigail has Pikachu run underneath a tree and fire a Thunderbolt straight up. Before Seviper bites, the hard Aspear Berry hits Seviper on the head and stops it. Pikachu fires Thunderbolt to send Seviper back and send Team Rocket flying. Abigail congratulates Pikachu as Ash and his friends arrive.
As they walk back, Theresa mentions that Abigail was a Coordinator in the Grand Festival. Knowing that Ash is heading to the Eterna Gym, Abigail asks for a battle, which stuns everyone. Theresa tries to talk her out of it, but Abigail is determined. Knowing that the battle would affect the disguise, Ash accepts. Back at the bakery, Ash is hesitant to battle, but Pikachu gives Ash a nod to let him know its ok. Ash brings out Aipom to battle, and although Aipom is stunned at battling Pikachu at first, Ash tells her that a battle is a battle and Aipom gets ready. Abigail tells Pikachu to dash, and Pikachu heads towards Aipom. Ash has Aipom use Double Team to surround Pikachu, but Abigail is able to counter this by having Pikachu jump up and fire a Thunderbolt down to create a blast of dirt, which cancels out all the copies. Ash, realizing that Abigail really knows how to battle, gets serious and has Aipom use rapid-fire Focus Punch attacks. Pikachu continually jumps backwards, eventually backing into a large rock. Aipom is about to land her first blow, but Abigail gets in front and the attack stops. Abigail forfeits the battle and congratulates Ash as she heads inside, leaving Ash stunned.
As night falls and everyone prepares for bed, Ash is worried that Abigail will be upset at learning the truth. He decides to tell the truth based on what happened in the battle. He heads off to find her. Abigail is out on the porch with Pikachu looking out to the moon. She mentions that the night was the same one when Sugar disappeared. Ash comes clean and wants to tell her the truth, but Abigail already knows. She mentions that how Pikachu got the Berries was different from Sugar's method. Sugar was not able to crack the Berries open, so Sugar left to find a way to get stronger.
Suddenly, a mecha arm steals Pikachu as Team Rocket shows up in another mecha, locking Pikachu in a cage. Pikachu's Thunderbolt is negated due to the cage. Team Rocket runs away as Ash jumps onto the mecha. The others follow in a van. Ash uses Staravia's Wing Attack on the mecha, but it's ineffective. The van catches up as Staravia attempts Aerial Ace. They jump a cliff and Ash falls off. The mecha fires another mecha arm to knock out Staravia. Team Rocket runs away as Ash recalls Staravia. The van cannot go off the cliff edge, as they appear to get away. Suddenly, a powerful Electric-type attack stops the mecha, but it appears outside. The light fades as they notice a Raichu. The Raichu scratches its head with its tail, revealing that Sugar evolved into a Raichu. They launch another mecha arm, but Sugar jumps to dodge it and uses Focus Punch to break the mecha arm and then uses dual Focus Punch attacks on the mecha exterior. After a constant battering, it breaks the hull open and Sugar gets inside, grabbing Pikachu's cage and escaping. Sugar fires a Thunderbolt into the exposed hold and destroys the mecha, sending Team Rocket flying.
The next day, the cake is finished and they sample the cake, finding it awesome. They congratulate Sugar for doing so well.