There's still a desert to cross before Ash can reach Veilstone City and the next Gym, but our heroes decide to let their Pokémon out to play in the sand. Pachirisu is right on top of a Hippowdon that surfaces from underground, and it falls right into Hippowdon's mouth! Hippowdon burrows back beneath the surface, so the chase is on to catch up with it as it pops in and out of the sand. Along the way, the gang runs into the Hippopotas they rescued a while ago. Is this Hippopotas looking for Hippowdon too?
Team Rocket is after Hippowdon too, but it'll take more than just a net to reel in a Pokémon this big and heavy. Unfortunately for everyone, the other Team Rocket, Butch and Cassidy, show up with a giant robot that ought to do the trick. Butch and Cassidy are out to grab a Hippowdon for Professor Nanba, but Jessie and James refuse to be outdone. It's not long before Jessie takes the controls of her mecha Slowbro and starts to slug it out with Butch and Cassidy's robot!
Ash and his friends try to lead Hippowdon to safety while the villains are distracted. Pachirisu is freed and Hippowdon wrecks Butch and Cassidy's robot with Hyper Beam, but then our heroes are caught between both Team Rocket teams! Hippopotas uses Yawn to put all the criminals to sleep, then joins forces with Hippowdon to send Jessie, James, Butch, and Cassidy far, far away. Now Hippopotas is happily reunited with Hippowdon and Pachirisu is back where it belongs!
Ash, Dawn, and Brock are walking through a desert on the way to Ash's next Gym battle in Veilstone City. Ash happily jumps down a hill and releases his Pokémon so they can play in the sand. Dawn and Brock both join him and let out their Pokémon as well. As they are playing, the sand rumbles up and a Hippowdon emerges from under the ground and lifts Pachirisu up on his back. Dawn looks him up on her Pokédex as Pachirisu climbs up to Hippowdon's head, and then Hippowdon yawns and Pachirisu falls into his mouth. Hippowdon then Digs back underground with Pachirisu still inside his mouth. As Ash and his friends quickly run after, they end up being too late and the Hippowdon is gone. Ash and Brock try digging in the sand but Pikachu points out a huge cloud of sand in the distance. Pikachu and Piplup run towards the big cloud of sand while Ash and his friends recall their Pokémon into their Poké Balls. Pachirisu appears out of one of Hippowdon's holes on his left side and is happy to see Pikachu and Piplup. Dawn quickly commands Pachirisu to get out of the hole. Pachirisu tries to wiggle free, but it finds out it's stuck and Hippowdon again digs underground taking Pachirisu with it.
Meanwhile, Jessie, James, and Meowth are digging a hole in the sand, trying to make their next trap, but the sand keeps falling back down and filling up their hole. Hippowdon then appears from underneath Team Rocket and blows sand out of one his holes. The sand blows Team Rocket into the sky and they fall into the sand somewhere in the distance. Shortly after, Ash and his friends arrive as Team Rocket watch from the distance. Dawn commands Pachirisu to use Discharge but nothing happens, while Ash commands Pikachu to use Thunderbolt and again nothing happens. Brock explains that Hippowdon is a Ground-type Pokémon, so Electric-type moves won't have any effect. Hippowdon once again digs underground taking Pachirisu with him once again. Jessie asks who that Pokémon was and James searches though some cards and finds out he was a Hippowdon. Team Rocket plans on then capturing Hippowdon, seeing as Pikachu's Thunderbolt had no effect on him, and then they plan to steal Pikachu afterward.
Ash and his friends try to find Hippowdon, but instead, Hippopotas appears from under the ground, and is very friendly. Ash realizes he might have been the Hippopotas they saved from a previous episode. Hippowdon then emerges from the ground and Hippopotas happily walks towards him. Pachirisu appears from Hippowdon's nose this time, and Hippowdon attempts to blow Pachirisu from his nose. This action just seems to anger him and he escapes to underground once more. Ash, his friends, and Hippopotas run towards Hippowdon and Hippopotas becomes really sad. Hippopotas really misses Hippowdon, so Ash lifts Hippopotas onto his shoulders and vows to reunite him with his old friend. Meanwhile, we see Team Rocket in a tree with binoculars searching for Hippowdon. They spot him and James takes out an RPG and fires a net at Hippowdon, capturing him. Team Rocket tries to steal Hippowdon but are unable to because he's too heavy. Ash and his friends catch Team Rocket in the act. Suddenly a Rhyhorn robot appears from underground with a big Team Rocket "R" symbol on it.
Out of the robot, Butch and Cassidy jump out and do their motto with a Shuckle. Jessie, James, Butch and Cassidy quickly begin insulting one another. Butch's and Dr. Namba's names keep getting mispronounced. Butch and Cassidy say they are there on orders from Dr. Namba to capture Hippowdon so he may analyze the sand. The four Team Rocket members keep arguing as Ash quickly commands Turtwig to use Razor Leaf to cut the net and they free Hippowdon. He escapes underground again as Butch, Cassidy, Ash and his friends quickly go after him--Butch and Cassidy in their robot and Ash and his friends on foot.
Ash and his friends hear Hippowdon but he's also being followed by Butch and Cassidy in their giant robot. A claw reaches out of the robot towards Hippowdon but Ash commands Pikachu to use Thunderbolt to stop the claw. Once more, Ash commands Pikachu to use Thunderbolt and it hits the robot, but it has no effect. Ash, his friends, and Hippowdon quickly run from the robot but suddenly fall into a very big hole in the sand. Jessie, James and Meowth are above them in their balloon and they do their motto. Jessie and James fire some sort of a plunger on a rope that captures Hippowdon and starts pulling him up into the air, but Ash and his friends grab onto it. Butch and Cassidy see this and fires a horn from the robot into the balloon and it pierces right through it, sending Jessie, James, Meowth, Ash, his friends, and Hippowdon falling to the ground. Butch and Cassidy yet again try to use a big claw from their robot to grab a hold of Hippowdon but Jessie, James and Meowth appear in a big Slowbro robot and break the claw. The two Team Rocket groups quickly begin to battle with their robots and arguing once again. As this is going on, Ash and his friends start running away with Hippowdon again. Jessie and James see this and fires Slowbro's tail as a rocket into Butch and Cassidy's robot, but it has no effect. Butch and Cassidy then again fire a horn rocket into the Slowbro robot and it drills though the robot and it explodes. The blast sends Ash, his friends, and Hippowdon flying into the air, and as Hippowdon falls onto the ground, Pachirisu falls out of his mouth and is reunited with Dawn and Piplup. Hippowdon is angered and fires a Hyper Beam at the Rhyhorn robot, making it completely fall apart.
After Butch, Cassidy, Jessie, James and Meowth recover, Cassidy sends out Granbull and Butch sends out Shuckle. Jessie sends out Seviper and it attacks Granbull right away. James sends out Carnivine. Cassidy commands Granbull to use Fire Fang but Jessie commands her Seviper to Wrap itself around Granbull, thus stopping its attack. Cassidy then commands Granbull to use Bite and Jessie commands the same attack with her Seviper and both attacks hit. James commands Carnivine to use Bullet Seed on Shuckle and it hits as well. Butch commands Shuckle to use Sludge Bomb but Carnivine ends up dodging and it hits Hippowdon. Ash sees this and commands Pikachu to use Thunderbolt and it hits Shuckle. Dawn commands her Piplup to use Bubble Beam and it hits Carnivine. Hippowdon is now angered and it charges at Team Rocket hitting Shuckle and Carnivine with Double-Edge sending both Pokémon at their respectful owners. Hippopotas then uses Yawn which makes Team Rocket, Butch, Cassidy, and their Pokémon fall asleep. It then follows it up by using Sandstorm which blows all Team Rocket members and their Pokémon into a group next to each other, while Hippowdon uses a Hyper Beam and makes them blast off.
Hippowdon and Hippopotas are finally reunited and Ash and his friends are very happy for them as the two play. Jessie, James, and Meowth are hanging from a tree angry at Butch and Cassidy. Butch and Cassidy are buried with the top half of their bodies in sand, and as they free themselves they are angry at Jessie, James and Meowth. Both teams vow their revenge as the episode ends with Dr. Namba yelling at Cassidy for pronouncing his name wrong.