Ash and friends are in a boat, still on their way across the ocean towards Mossdeep City. Max notices from the Pokenav that there are three islands just ahead. Brock has apparently looked it up already, so he explains about the Ha-Ro-I islands, and mentions that I Island has a Pokemon Center. A couple of Wailmer follow them briefly as they head for the islands. Suddenly, a bunch of kids race by them, riding their Huntail and Gorebyss. Ash and May check out Huntail and Gorebyss in their Pokedexes, and learn that they both evolve from Clamperl. Turning their attention back to the race, they see one girl get knocked off her Huntail. Ash & co stop to see if she’s ok. She is, and she resumes the race. Then, a young boy and girl go by on little pedal-boats, deep in an argument. The boy thinks Huntail is better than Gorebyss, while the girl believes the reverse. All of this has aroused the curiosity of Ash & friends.

Meanwhile, not far away, Team Rocket is pursuing the “twerps” as usual, in their Magikarp sub. Suddenly, they get stuck between two boulders underwater. They start pedaling at full power to try and break free, but the sub’s hull buckles, letting water gush in.

By now, Ash and friends have reached the Pokemon Center, and greet Nurse Joy. Brock flips out as usual, and Max drags him away. After a brief interruption so Joy can accept a call and a transported Corsola from another trainer, the group suddenly hear loud voices arguing. Turns out that this Nurse Joy is also a teacher, and her students have begun arguing in her absence over whether Huntail or Gorebyss is better. Joy quiets the kids down, then takes everyone out to the pool, much to the kids’ delight. On the way, Joy explains about the rivalry between the Huntail trainers and the Gorebyss trainers on these islands, and the regular water races they have.

At the pool, the kids (including the two from the beginning of the episode) are watching two Huntail and two Gorebyss swim around a man floating in the pool. The man turns out to be none other than Professor Birch! Joy is surprised to learn that Ash and friends know the Professor, and greetings are exchanged. May assumes he must have been doing some sort of research in the pool with the Huntail and Gorebyss, but Birch says he was just playing with them for now. Birch explains that he’s here to learn more about what makes Clamperl evolve into Huntail or Gorebyss. Birch fields a couple of questions from the kids, then explains that Clamperl evolve using either the DeepSeaScale or DeepSeaTooth, and produces models of the items to show the kids. He goes on to explain that he had heard that when Clamperl are placed in the water in the two other islands, they tended to soon evolve into either Huntail or Gorebyss, so he suspects he might be able to find the DeepSeaTooth and DeepSeaScale on those islands. Ash says he and his friends would love to come along, and Birch agrees to let them come.

A scene change later, they’re in a speedboat, ready to take off for Ha Island. Namiko (the young girl from earlier) joins them at the last minute. Unbeknownst to them, Kikuma (the young boy from earlier) is following in his pedal boat. Having reached Ha Island, Birch tastes the water from a waterfall inside a cave there. Just as he suspected, the mineral content seems very high, so he takes a water sample. Suddenly, the sound of a footstep behind them betrays the presence of Kikuma, much to Namiko’s annoyance. Kikuma is anxious to evolve his Clamperl into a Huntail, and had been eavesdropping. Birch explains that he fully intends to investigate *both* islands, and Kikuma accompanies them to Ro Island. This time, Namiko follows in the pedal boat. Same process here. Birch tastes the water, takes a sample, and Namiko accidentally betrays her presence. This time it’s *her* turn to eavesdrop on the enemy.

Back at the lab on I Island, Birch analyzes the water, and finally thinks he has the scientific stuff figured out. Kikuma and Namiko run up to the group, anxious for news, and argue briefly before May and Birch calm them down. Birch asks to see their Clamperl, so they all go out by the pool, and the kids send out the Clamperl. Birch says they look healthy, and if everything works out, they should each be able to evolve.

Meanwhile, Team Rocket has made it to the pool (it has an opening to get in and out from the ocean) and they’re watching the scene from their sub. Meowth wants to give all the Huntail and Gorebyss to the Boss, and has a vision of him riding them like waterskis, similar to how the locals do it, except the Boss is riding both at once. James is skeptical, but Meowth insists, and Jessie likes the plan as well.

As the group continues to talk by the pool, TR suddenly makes their appearance, and they say their motto. They send a net out from their sub to catch the Huntail and Gorebyss, but Ash quickly sends out Corphish to cut the net. Jessie sends out Seviper, who attempts a Bite attack. Corphish counters with Harden, and Seviper just ends up hitting its head. Ash then orders a Crabhammer, and Corphish uses it to slam Seviper into the water. James sends out Cacnea, who after hugging James as usual, fires a Pin Missile at the Clamperl. The kids tell their Clamperl to use Iron Defense. The Clamperl close their shells, and the pins just bounce off. Jessie orders a Poison Tail, and Seviper jumps out of the water, but Corphish counters with Bubblebeam. Both Clamperl then use Water Gun together, sending Seviper and Cacnea back to the sub. Finally, a Thunderbolt from Pikachu sends TR blasting off. The kids celebrate, and the Professor says it’s now time to go look for the evolution items.

They go back to Ro Island to look for a DeepSeaScale. Kikuma finds it, and gives it to Namiko, who in turn gives it to her Clamperl. She expects an evolution, but nothing happens, so Birch suggests sending Clamperl to the Pokemon Center, since Clamperl won’t evolve right away when given the item. The girl agrees and they do so from the cabin on the island. On Ha Island, they again search, and find a DeepSeaTooth. Fittingly, Namiko finds it, and gives it to Kikuma, who gives it to his Clamperl. His doesn’t evolve right away either, so he sends it to the Pokemon Center as well.

Back at the Pokemon Center, the kids receive their Clamperl from Joy and send them out. They haven’t evolved yet, and Birch is briefly puzzled, but then they start to glow, and evolve into Huntail and Gorebyss! The kids take their newly evolved Pokemon out to the pool and watch them swim for a bit. Suddenly, TR shows up again, this time in a giant Kingler mech. Meowth sends one of the mech’s claws at Gorebyss. Namiko tells Gorebyss to dodge, and Kikuma tells Huntail to try a Bite attack. Huntail charges forward, but just bounces off the mech. Ash sends out Grovyle to use Bullet Seed, but to no avail, as that bounces off as well. Huntail and Gorebyss use a combined Water Pulse, which knocks the mech back briefly. TR quickly recovers and Meowth fires a claw at the two Pokemon. They dive in the water to dodge, but a net from the other claw catches them when they resurface. However, Grovyle promptly uses Leaf Blade to cut the net and free them. Namiko orders a Confusion from Gorebyss, and it levitates the mech. Kikuma takes the opportunity to order a Screech from Huntail. Pikachu then uses Thunder to blast off Team Rocket once more.

Now that the danger is gone, the kids admire how well their Pokemon worked together. May suggests that maybe now their feud can end, and the kids agree. Nurse Joy then calls to them, saying their boat is ready to leave. As the boat sets off, everyone shouts their goodbyes. Kikuma and Namiko, riding their Huntail and Gorebyss, catch up to the boat and tell the group that the Huntail and Gorebyss trainers have finally patched things up, now that they understand more about their Pokemon. After hearing this pleasant news, Ash and friends wave goodbye to the kids, as their boat rides off into the sunset, proud to have had a hand in solving another Pokemon mystery.

Thanks To Geodude For Writing this for us