Ash and co. have found a river in Dewford Island. Max thinks that they will find some rare Pokémon if they keep on following the river. Ash likes the "rare Pokémon" part because he can keep up with his training and find some rare Pokémon. They are following the river to find a new training spot. May shapes her hands as a video screen. She is pretending to be a TV Reporter. Suddenly, the group finds their path blocked by a waterfall. Brock thinks that the rare Pokémon are on top of the waterfall. He sends out Lotad. Then Brock takes a rope with a rock on the end of it. He throws it and Lotad uses Water Gun to push the rope around a tree. Afterwards, Ash and co. begin to climb the waterfall using the rope. May is already at the top of the waterfall. She helps pull Ash, Brock, and Max up. Apparently, May used Silcoon's thread to help herself up.

The group notices that the water is much more calm at the top. They continue to walk. Brock notices the ground has gotten to be more muddy. Up ahead lie several Mudkip. Ash looks up Mudkip in his Pokédex. On a rock are two Mudkip that were just born. May remembers her first experience with Mudkip. Now she thinks the Mudkip are cute. Brock explains that Mudkip are rare Pokémon. May wants to capture one. She runs towards the Mudkip. A bigger Mudkip comes out and uses Water Gun on May's face.

Suddenly, one of the baby Mudkip falls in the river. It begins to flow downstream to the main current. Brock sends out Lotad to save the Mudkip. Lotad swims and catches up with the baby Mudkip. However, Lotad is now stuck as it is now floating downstream. The bigger Mudkip from before jumps in the river and pulls Lotad to dry land. Brock walks over to the Mudkip. The Mudkip are bit scared of Brock, but Brock holds out his hand to the Mudkip and assures it that there is nothing to be afraid of. Ash, May, and Max meet up with Brock.

Someone then comes out of the bushes. May at first thinks it's a monster, but Max reassures her that it's a person. The man thinks Ash and co. are stealing the Mudkip. Ash tells the man that they would never steal the Mudkip. They were just saving one of the Mudkip that fell in the river. The man believes Ash's story. Then he introduces himself as Swampy to Ash and co. Swampy wonders how Ash and co. were able to get past the fence. Ash and co. tell him that they took the river entrance up to the place. Then Swampy offers them some tea back at his place.

Swampy says that his place is usually where the Mudkip are raised. Brock sees four blue things and asks Swampy what they are. The blue things happen to be Mudkip eggs. Ash and co. are happy to see the eggs since they never have seen them before. Then they wonder where Swampy gets the eggs from. It is suppose to be a secret, but Swampy his secret to them. Swampy gets the eggs from the Pokémon League and then raises the eggs himself. Brock mentions to Swampy that he is a Pokémon Breeder. Swampy offers Brock a chance to see a Mudkip hatch from its egg.

They go to a nest with three eggs. One of the eggs hatch into a Mudkip. May really thinks the baby Mudkip are cute. Brock tells Swampy that it was actually an older Mudkip that saved his baby Mudkip. Swampy says that the older Mudkip is actually a wild Mudkip who likes to sneak in sometimes and protect the babies, however it is too big for the place. Swampy wants to find a trainer who can take care of the Mudkip, otherwise it won't have any friends.

Team Rocket is walking through the grass. They come across a fence. Meowth wants to know what a fence would be doing in this place. James says that someone obviously doesn't want them trespassing. James thinks someone has something rare and valuable. Team Rocket's eyes light up. Jessie sends out Seviper and James sends out Cacnea. Seviper uses Poison Tail on the fence, but it doesn't break. Cacnea uses Needle Arm, but it uses the attack on James. James slams right through the fence and breaks it.

Swampy hears the alarm sound. They run over to see what happened. Brock sees the Mudkip from before. Brock says hello to the Mudkip, but it runs away. Brock chases after it. Brock follows Mudkip to another part of the forest. Brock wants Mudkip to come with him, but Mudkip still doesn't trust Brock. Brock then holds out some Pokémon food for Mudkip, but Mudkip doesn't eat it.

Ash, May, Max, and Swampy run to the front where the fence is at. They see the fence is totally destroyed. Team Rocket pops out from behind the bushes. They say their motto. Ash tells Swampy that Team Rocket are the bad guys, and that they want to steal the Mudkip. Team Rocket dreams about capturing all of the Mudkip and being executives. Swampy has a problem with being secretive. He always gives out secret information. He accidently tells Team Rocket that by breaking the dam that holds the water will flood the place leaving the Mudkip defenseless. Team Rocket hears this. James sends out Cacnea and tells it to use Needle Arm. Cacnea hits James with Needle Arm. James flies through the dam. The water begins to rush out.

Brock also notices the strong current of water. He sends out Forretress to stop the water from getting any closer. While Forretress is holding back the water, Brock, the bigger Mudkip, and Lotad help rescue the baby Mudkip. When Forretress can't hold back the water anymore, it returns to Brock. Then they all go to higher ground. However, down below is still one more baby Mudkip. The bigger Mudkip jumps into the water to save the baby. It grabs onto the baby, but the Mudkip can't resist the current. It is headed straight for the waterfall. Both Mudkip fall down the waterfall, but the bigger Mudkip is holding onto a rock that is extending out of the waterfall. Brock finds the rope that he used earlier. He ties himself the rope and jumps into the water. Brock holds his hand out to the Mudkip. Mudkip has no choice but to trust Brock. It holds out its fin to Brock. Brock grabs hold onto Mudkip and the baby. Ash and the others pull Brock up.

Suddenly, the group hears a noise coming from the swamp. It is Team Rocket in their new machine. They are searching for the Mudkip. They begin to scoop up the Mudkip and place them in a bag. Ash demands Team Rocket to stop stealing the Mudkip. Brock notices that the feet to Team Rocket's machine is sinking in the ground since the ground is very soft. He tells Lotad and Mudkip to use Water Gun on the ground. This way Team Rocket will get stuck. Mudkip and Lotad obeys Brock's orders. Team Rocket make a joke that the Pokémon are helping them "grow." They suddenly realize that Ash and co. are trying to make them sink. Team Rocket can't move at all. Mudkip then tackles the bag, freeing all the baby Mudkip. Afterwards, Pikachu uses Thunderbolt to blast Team Rocket off in the sky.

Brock thanks Mudkip for doing a good job on saving the baby Mudkip. Ash and the others notice how close Brock and Mudkip have become. Swampy wants Brock to take the Mudkip along with him on his journey. Brock thinks it's a good idea. Brock asks Mudkip if it wants to come with him. Mudkip decides to come with Brock. It happily jumps in Brock's arms. Now that Brock has a new Pokémon, Ash continues his training for his Dewford Gym rematch.