The gang continues their journey through Izabi Island, though they encounter a desert. Brock's map and Max's PokéNav have no data about the desert, and yet there are many holes around. They do notice every hole is the same size. Ash throws a rock into the hole and a Pokémon is seen eating the rock - a Trapinch. There must be more Trapinch, as there are many holes around. However, they hear a police alarm and a woman comes to them. The woman tells them they are trespassers, and they must leave, as the area is dangerous. Despite that, Brock flirts with her. The woman gets out of the flirting and introduces herself as Elisa. Brock does not stop flirting, so Max pulls his ear. Max and Ash apologize. Ash goes around and he falls down a hole.
Elisa gives him a rope and Elisa pulls him up. The holes underneath hide a cavern full of Trapinch. Elisa and the others wanted to move the Trapinch, but they dig more, so nothing could be done about it. Elisa takes them somewhere safe, but during the travel, they see a man running away from an angry Donphan. The man recognizes Elisa, for some reason. Elisa calls Meganium out, who uses Sweet Scent to calm Donphan down, so Elisa calls Meganium back. The man is grateful - Elisa introduces him as Hal, the Izabi Island researcher. Hal shows that it was looking for the Trapinch - with a transmitter. Hal begins to explain them the situation with Donphan, while Team Rocket spies under the earth, using a periscope from a Diglett machine.
Hal tells them that the transmitter will tell them the location of an underground lake. The gang wants to hear about this lake, so Hal tells them what it is. Hal tells them that one day he fell into a hole and when he woke up, Hal saw a large, beautiful underground lake - with a lot of Trapinch as well. However, he remembers that Trapinch evolved into Vibrava - he followed them and found himself out of the lake, but did not remember how he got out. The gang is amazed by the story, but Elisa thinks Hal made that up. Hal tells them he became a Trapinch researcher for that. However, Max spots Trapinch with the transmitter is gone. May spots it is going into the hole. Soon, they feel vibrations - Team Rocket appears in the machine, capturing Pikachu. Pikachu uses Thunderbolt, but with no use.
Brock sends Ludicolo (who dances with Max), who uses Water Gun on the machine. The machine begins to be destroyed, though Pikachu is dragged down as well. The Trapinch appear and eat the metal from the machine. The Trapinch eat the machine pretty damn quick, but Team Rocket and Pikachu are dragged down into the hole. Ash, Elisa and the Trapinch with the transmitter come down as well. Pikachu, Team Rocket and Ash, Trapinch and Elisa split. Brock, May and Max stay outside, though they need to find a way to help them. Hal discovers a signal of Trapinch, so he goes down. Despite the warnings, Hal falls down into the hole. Hal falls down and goes after the signal. Ash tries to find Pikahcu, but with no success. The Trapinch goes down a path, so they follow it. Team Rocket go down a path and see a Trapinch, so Meowth thinks it will open the nuts for the boss if he had one, so they go to capture one. However, it has gone away, so they hide when they heard some steps.
The steps are Hal's, so they go to follow him, going after the Trapinch he is following. Brock, Max and May are worried. Max goes to the edge and nearly falls, but May got him and Brock got her. However, they are both heavy, so they all fall down. Ash, Elisa and Trapinch go to find Pikahcu and see May, Max and Brock falling down. Ash asks where Hal is, so Brock tells him he was looking for the Trapinch with the transmitter. The Trapinch is eating rocks to make a path. Elisa hears something - it is the water going through the path! The gang runs, but the water gets them and leads them to the lake Hal spoke of. Pikachu arrived before, so Ash goes to him. They also see the Trapinch with the transmitter and Hal following it. Team Rocket hides and plans to take Pikachu as well.
Hal tells Elisa that it is the lake he spoke of. Elisa replies she thinks she is a fool not to trust him, but Hal tells her that she did believe him. The talk is interrupted when Brock sees the Trapinch gathering. The Trapinch evolve to Vibrava. Jessie and James are sad they couldn't capture them, but Meowth tells them they are part Dragon, so it means they are quite worth. The Vibrava fly off, though Team Rocket capture them all. Brock sends Ludicolo and Elisa Meganium. Ludicolo attacks with Bullet Seed and Meganium with Razor Leaf - the Vibrava are free.
Jessie sends Dustox and James Cacnea. Dustox attacks with Poison Sting and Cacnea with Pin Missile, though the Vibrava stand in their way, negating the attack with Supersonic. Pikachu blasts them off with Thunderbolt. Now, the gang would have to get out. However, they are carried up by the Vibrava. Vibrava fly off and the gang waves goodbye at them. At the end of the day, Elisa gives them directions to the nearest town. Hal decides to keep the lake a secret - he wanted to find it - along with Elisa.