At the Pokémon School, Ash asks his classmates what their plans are for the upcoming holidays. Sophocles invites everyone to a fireworks display on Melemele Island, but Lana perks up and says that the class has some special guests. To everyone's surprise, Ash's old friends Misty and Brock arrive at the school. Lana explains that she and Misty had been writing to each other since the school excursion to Kanto. Ash asks about the Cerulean Gym, but Misty explains that her older sisters are taking care of it while she is away. She then informs everyone that she and Brock want to tour Alola, and Ash and his classmates agree to show them around.
At a local Pokémon Center, Brock tries to flirt with Nurse Joy, but Misty pulls him away by the ear. Suddenly, a young Trainer runs into the Center and tells Nurse Joy that his Yungoos hasn't eaten all day. Nurse Joy takes Yungoos in her arms for a closer inspection and is surprised when Brock instantly sees the swelling in its jaw. As she, her Blissey, and Comfey prepare to take Yungoos into surgery, Brock offers his assistance. Joy accepts, and he bids Ash and the others farewell as they continue their tour.
Inside Bewear's den, as Bewear feeds the Team Rocket trio and Stufful some honey, James realizes they need to make an urgent call to the Team Rocket HQ. The trio makes the call, but it is instead answered by Matori's Alolan Meowth. Meowth translates the Alolan Meowth's comments, but is left infuriated by its dismissive manner. James agrees with Meowth's comments that they haven't achieved anything noteworthy, but Jessie adds that their Malasada business has seen increasing sales. Meowth explains that to Matori's Meowth, but the transmission is cut off suddenly. This leaves James worried that Team Rocket may have forgotten them. The trio soon realizes they are becoming less notorious and fear that the Malasada business will be their reality. Meowth is reinvigorated and declares that they will aim to show up Team Rocket with their explosive efforts.
Misty and the others sit down for a meal at the Hau'oli City Pancake Parlor. Nina's Alolan Raichu presents everyone with their orders; towering stacks of pancakes and refreshing drinks on the side. Nina and her new husband, as Mallow reveals, also attend the groups table. After finishing their meals, the group makes their way over to the Hau'oli marketplace to meet Anela. As Misty's admires Anela's bountiful produce, Psyduck emerges from its Poké Ball and swallows a watermelon whole. Misty apologizes for Psyduck's behavior, but Anela simply laughs and goes on to offer the group a plate full of fruit. The group then visits the mall, where Misty and the other girls look through a jewelry store. Misty then calls on her Corsola to look at some Corsola horn pendants, but the Coral Pokémon is horrified by the jewelry display. Lana goes on to joke that the pendants are made from actual Corsola, making Corsola even more scared. Ash, Sophocles and Kiawe wait on a roof deck for the girls to finish their shopping, they spot two Mantine Surfers performing tricks out at sea. Rotom explains that Mantine Surf is a type of Poké Ride. The girls meet up with the guys, and together they decide to go Mantine Surfing. Ash then suggests they head to nearby Treasure Island, he adds that he and Pikachu enjoyed the place when they last visited it. Team Rocket overhears the plans and sets their sights on stealing all of the Mantine and Pikachu to send to the Boss.
As the group surf across the ocean, Rotom informs Ash that jumping is part of the fun of Mantine Surfing. Sandy's old friend Mantine arrives on the scene and prompts Sandy to hop on its back. Lana is initially surprised as Sandy and Mantine go on to perform a jump on a wave. The impressive display encourages Ash and the others to perform their own Mantine Surf tricks. Meanwhile, Brock finishes bandaging up the injured Yungoos's jaw. Joy shouts out that it is wonderful, but when Brock turns around he quickly realizes that she is just talking about a Luxray's soft coat.
Ash and the others arrive on the shores of Treasure Island. As Misty tells the Mantine to hang around while they explore, Ash is eager to show everyone around the island and runs off. The group arrives in a flower meadow and admires the Bug types. Lana realizes that Misty is gone, but everyone soon spots her cowering behind a tree in fear of the bugs. Ash's friends, a horde of Alolan Exeggutor then arrive on the scene, much to everyone's surprise. The group soon enjoy a ride atop the heads of the Exeggutor before taking a dip in a local watering hole. Lillie and Snowy rest in the shade, while Psyduck and Marowak quickly get out the water as everyone else plays with the Exeggutor. By the day's end, the boys are spread out on the beach sand in exhaustion as Lillie and Mallow make a sandcastle. Meanwhile, Lana approaches Misty as she sits by herself admiring the ocean view. As Misty declares it is time to head back, a sudden explosion occurs.
Sandy leads everyone to Team Rocket, who have since caught the Mantine in a net. From inside their newest mecha, the Giga Meowthbot 3, the trio performs their motto. Misty is shocked to see them in Alola, but Jessie says they are simply following Giovanni's orders. James pulls a lever and the net full of Mantine is winched inside the mecha's body. The trio then turn their attention to catching Pikachu. Pikachu's Thunderbolt and Marowak's Bonemerang prove useless against the mecha's metal exterior. James and Meowth explain that the Meowth Giga Robot Mark Three is a cut above the rest, and Jessie demands that everyone simply give up. Sandy uses Double-Edge to open the Meowth mecha's hatch, but with a little effort while Ash and the others prepare for a joint retaliation. Misty sends out her Gyarados, and the giant Pokémon then wraps itself around the mecha. Pikachu's Iron Tail causes a minor explosion and hole in the robot's body. Popplio and Sandy then hit this same spot with Aqua Jet and Double-Edge.
Meowth, strapped up with a motion control device, has the mecha fire rocket fists. Tsareena and Marowak use Trop Kick and Iron Head to deflect the fists away from the group. Then, Pikachu's Iron Tail, Togedemaru's Zing Zap, Sandy's Double-Edge, Popplio's Aqua Jet, and Snowy's Tackle break open the Meowth mecha and release the Mantine. Tsareena uses a Magical Leaf to free the Mantine from the net. Team Rocket are infuriated and fling Misty's Gyarados off the mecha. In response, Misty Mega Evolves her Gyarados into Mega Gyarados, much to Team Rocket's shock. With Gigavolt Havoc, Inferno Overdrive, and Hydro Vortex, Ash, Kiawe and Lana have Pikachu, Marowak and Popplio perform their respective Z-Moves on the Meowth mecha. Team Rocket remain defiant as the mecha is able to cope with the combined onslaught. Misty has Gyarados add Hydro Pump to the mix, causing the robot to subsequently explode and send Team Rocket blasting off again.
Later on, Misty joins Ash, Rotom, and Pikachu for a seaside walk. The pair soon spot a green tent and Brock cooking up a delicious meal. They ask Brock about the setup and he explains that it because they are all together again. As Brock turns his attention to his boiling stew, Psyduck pops out of its Poké Ball, eager to get the first bite.