While at the boat towards Lily of the Valley, Ash cannot wait for the League to start. Piplup notices a ball and goes for it, but bumps into a Baltoy. Its trainer comes and is a bit annoyed, so Dawn and Piplup apologize. The trainer is Buck, while the heroes introduce themselves. Ash tells him they are on their way to Sinnoh League, while Buck responds he is here as a treasure hunter. He will have his Baltoy search for treasure, which gets Team Rocket's attention, who are serving as waiters. Buck knows that Baltoy can search for treasure and when he discovered the pirate ship, he spot a chest, but was empty.
Although he did not find anything, he got a map, where the pirates must have stored their treasure, on Dandylion Island. On the back side is a spot of the mountain, where the treasure must be, even if Brock's Pokégear does not show anything but a forest. What Buck does not understand is why are Pokémon drawn on the map. Though they recognize Vileplume, Voltorb, Pineco and Graveler, they don't think there is any connection. They do recognize Lunatone and Solrock, but do not know what that means. Buck offers them an expedition to search for treasure, which everyone agrees to. Team Rocket also plan to get the treasure... first.
As they go towards the mountain, Piplup wants to go there before. As he goes, he gets blown away by a Voltorb, as they explode. Pikachu uses Thunderbolt and stalls them, as they all get away. While they went away, Piplup continues to go towards the mountain and gets ambushed again, this time by Pineco. Though they did get away, Buck suspects the Pokémon on the map are actually traps, preventing their progress towards the mountain. Knowing Graveler and Vileplume, Ash, Brock and Dawn know Piplup and Infernape will be able to stop these Pokémon traps. Team Rocket also go towards the mountain and get ambushed by exploding Voltorb. Piplup goes ahead and gets bounced off by a Vileplume, as he wakes them all up. Gloom and Vileplume use Acid, so Ash sends Infernape, who uses Flamethrower to scare them off. Brock treats Piplup and gives him medicine, which gets the Stun Spore off.
Team Rocket got to a portion of the forest and get attacked by exploding Pineco. The gang came to the mountain and has to take a direction. Piplup chooses one, but Buck's Baltoy shows another path, in which everyone goes to. Team Rocket encounter Vileplume and Gloom, who use Acid on them. Jessie sends Seviper, who charges through using Poison Tail. Team Rocket follow it and pass through. In the cave, Baltoy shows the path. Graveler roll towards them, so Piplup uses Hydro Pump to get one of them away. however, he gets hit by one of them, so the gang runs. Ash, Dawn and Brock fall into a deep cavern, but get separated from Piplup, Buck and Baltoy. Golem appears and while they have not seen it on the map, Ash sends Gible, who uses Rock Smash and makes it run away.
Though separated, Gible knows of a way. Dawn wants Ash to call Gible off, but too late; Gible uses Draco Meteor and while it fails, it lands on Piplup. While Buck is surprised, he soon gets founded by Ash, Brock and Dawn. Piplup is irritated, but is told that was a way to find him and gets less angry. Team Rocket also came to the caves inside the mountain and Meowth picks a way. When he climbs to one of the paths, he soon wakes up an Onix, who blasts him, Jessie and James off. The gang found a path away, but soon find a temple, which is where Buck hopes he will find the treasure. They find paintings of Solrock and Lunatone and another, stranger one.
Baltoy is pointing at a triangle, which Brock suspects it might be a trap. Team Rocket invade. Meowth accidentally presses on the triangle, which releases a Claydol. Dawn realizes the patterns on the top of the temple are Claydol's, which Buck suspects Claydol guards the treasure. Jessie sends Seviper and James Carnivine. They use Poison Tail and Bullet Seed, but Claydol evades and becomes angry; it spins and blasts them off. Claydol turns to the gang, so Piplup uses BubbleBeam, but due to LightScreen Claydol used, the damage is reduced. Claydol uses Ice Beam, which freezes Piplup, but gets unfrozen soon enough. Claydol uses Psybeam, but the heroes evade. Ash sends Torterra, who uses Leaf Storm, but gets deflected. Torterra uses Energy Ball and misses. Buck decides to give it a try, as Baltoy evolves into Claydol.
Baltoy uses Shadow Ball, but LightScreen reduces damage. Claydol uses Psybeam and hits Baltoy. Baltoy retaliates by spinning around Claydol using Gyro Ball. While Claydol attempts to retaliate, it misses and gets hit by Gyro Ball. Using SolarBeam, Baltoy hits Claydol and continues to hurt it using Gyro Ball. Buck throws his Poké Ball and catches Claydol. A counter rises up and opens, revealing a bunch of vases, pots and cups. While Ash, Brock and Dawn are not impressed, Buck is more than happy, as he now has treasures to study as an archaeologist, something he wants to become. At the ferry, Buck says he will get aboard a new boat for a different location and wishes Ash luck in the League. After waving goodbye to Buck, Brock, Ash and Dawn know that the Lily of the Valley is not far ahead.
- In the scene where Carnivine is seen to be biting James' head, the white part above Claydol's "beak" disappears.
- When Dawn catches Piplup after Claydol uses Ice Beam on him, Dawn's hands are larger than they should be.