The episode begins with our heroes walking through a forest, with Max leading the way through the seemingly never-ending road to their next destination. Ash, eager to challenge his next opponent, asks Max if the Battle Pyramid really is along this path since they've been searching for quite a while now. Max, checking his PokeNav, says that they should be seeing it anytime now... and, at that moment, the top of what appears to be a large Pyramid looms over the horizon, above the tops of the trees before them. Ash wonders if that could be what they are looking for, and Max confirms that it is indeed the Battle Pyramid, and part of the Battle Frontier Challenge. Ash thrusts his fist in the air in excitement, and says that they should head towards there straight away. May remarks on his excitement, and reminds him about her Grand Festival. The group continue to walk towards the building, but suddenly the ground beneath them gives way, the stones crumble and the group is sent falling into darkness!

After some time, the group eventually come to after their long and hard fall. May wonders what possibly could have happened, and Max says that he bets it's something to do with Team Rocket. Brock doesn't think so, and looks around at the walls around them... this is not some pit dug by Team Rocket. Markings of ancient Pokemon cover the walls. May wonders how they can get out, and looks upward to see that there is no possible way to get out the way they came in. Max sees a light in a far off passage, and suggests that the group go that way to see if they can find an exit somewhere. Ash agrees, and the group walk off down the passageway. Elsewhere, we find Team Rocket looking at the hole the group fell down, and Jessie wonders what possibly could have happened to make it give way like that. James observes the area around the hole, trying to work out the reasons for the collapse. Wobbuffet then screams its name as usual, and that seems to spark something off, as large cracks appear on the floor beneath them to. Realising what is happening, Jessie screams that they should run, but before Team Rocket can do so, the floor breaks beneath them and Team Rocket fall into the same dark hole that Ash and co. did.

Back with the group, May and Max point out a Pikachu statue on a pedestal near them. Ash runs over to it, and remarks on how cute it is, and is about to touch it before Max shouts at him not to. Not only is it ancient, but it could also be a trap. Ash says that it'll be okay, and nothing to worry about at all, and picks the Pikachu up anyway. Removing the statue seems to trigger something, and its eyes begin to glow, as do the eyes of the Pikachu on the stone door in front of them. Ash is about to put the statue back, but the stone door slides up and reveals a huge boulder which instantly starts to chase after them down a tight passageway. They continue to run, and soon see a middle aged man with brown hair, and wearing a green outfit in front of them. Ash screams at the man to get out of the way, and the man mutters that they must have set off one of the traps. At that, he grabs a Pokeball at his belt and calls out the Legendary Regirock. With Regirock out, the man orders his Pokemon to use Focus Punch, whch it does, smashing apart the boulder and saving Ash and co. Ash mutters that that was amazing, as May checks Regirock on her Pokedex. The man then returns Regirock to its Pokeball, and Ash remarks that the 'old man' was amazing. This provokes an angry reaction in the man, who says that he is not an 'old man', but Brandon. The group thank him, but Brandon asks them why they have trespassed here.

May explains that they didn't mean to, and that they simply fell down a hole which appeared when the ground beneath them crumbled. Ash then apologises for setting the trap off, to which Brandon asks if he is a Pokemon Trainer. Ash says that he is, and Brandon snaps, saying that since he is a trainer he should not have made such a foolish and deadly mistake. Ash grits his teeth in frustration, and Brock asks what Brandon is doing here himself. Brandon explains that he is here as a protector and researcher of sorts of an ancient culture which lays buried deep down underground. Max seems to know what Brandon is talkin about, and says that he heard about such a place once before while struggling to remember the name. Brandon then calls the ancient civilisation 'Pokelantis', which provokes a gasp from the group. Brandon then briefly explains about Pokelantis, and an evil king which corrupted it and perhaps was responsible for its eventual downfall. Listening to all of this behind a pillar is Team Rocket, who suck up all the information about Pokelantis in excitement. James remarks that this could be their big break... just think about all the treasures that could be found down here! The group recite their usual promotion chant, and run off in search of the riches.

Back with Ash and co., Brandon suggests that they stop playing around and leave. Ash says that they aren't here to play around, and that he is here to win a Frontier Symbol from the head of the Battle Pyramid. Before Brandon can ask him further about wanting a Frontier Symbol, Ash storms off, dedicated to finding the Frontier Brain and obtaining his last Symbol. Meanwhile, Team Rocket find themselves in a similar passageway that Ash and co. found themselves in before the huge boulder began to chase after them. Much like Ash, as soon as Jessie sees a statue of a Smoochum, she just has to grab it and start to huggle it. However, much like Pikachu with Ash, the statue triggers a door with a Smoochum to slide open and reveal another large boulder which instantly starts to roll after them. Back with Ash, we find him as he comes across a door with several strange symbols on them. He starts to touch the door, trying to get it to open when it spins around and carries him to the other side- the side he was trying toget to. At that moment, May and Max run up to the door after seeing Ash taken away by it. They pound on the door to try to get it to open, but no luck. May asks Brandon what they should do, and Brandon mutters that they'll have to do something, otherwise Ash could be in serious danger.

On the other side, Ash gets up and instantly all the torches start to light up around him, revealing from the darkness a large statue of a big man holding a sceptre. In front of the incredibly large statue is a throne which upon it, lies a stone Pokeball. Ash picks the Pokeball up, and wonders if there could be anything inside. As he thinks, Brandon pulls away a stone from the other passage and presses a secret button which was inside. The doors open, but just as Brandon and the rest of the group are about to stop Ash, Ash is already holding the Pokeball up and calling out the creature inside. At his words, the Pokeball begins to shake and a booming voice calls out from inside it. There is a blinding light, and when it clear, a strange dark vapor appears out of the Pokeball and circles Ash, before going inside him. Ash falls to the ground in shock, and May asks him if he is okay. Ash gets up, but instead of replying, starts to laugh evilly.

Somewhere else in the Pyramid, we find Team Rocket standing in front of yet another door trying to decide whether to go in or not. Meowth looks through the keyhole, and simply sees the wings of one lone bird Pokemon. At that, Jessie and James tug on the doors and pull them open, but are soon sent running when a Pidgey starts to chase after them for disturbing its room. Back with Ash, the group look on as Ash, who appears to have been possessed by the darkness from the Pokeball, tells them that he is finally free... and with his freedom, he requires power, and Pokemon. Darkness then comes from Ash's body and tries to take the group's Pokeballs away, but they manage to grab them in time. Max asks what is up with Ash, and Ash asks who that is, because he is the great and mighty ruler of Pokelantis! Brandon mutters to himself about Pokelantis, as he remembers the legends about the corrupt ruler of Pokelantis and how he had to be locked away. Brandon then walks towards The King, and explains who he is: Brandon, he Pyramid King. The group gasp in shock, and Brandon continues to challenge The King to a Pokemon Battle in order to settle the situation. If Brandon wins, then Ash will be left alone, but if The King wins, he can have what he wants. The King laughs, and agrees to the terms. Meanwhile, Team Rocket have come across a dark tunnel. Meowth shouts 'Hello' down the tunnel, and his voice echos throughout. Seeing that the coast is clear, the group then run down the tunnel reciting their Promotion chant. However, the coast wasn't as clear as they thought, as a Salamence appears around the corner to the tunnel, and fires out a Flamethrower which sends Team Rocket running in the opposite direction.

Outside, the group are surprised to see Scott who came to see Brandon, waiting outside the proper Battle Pyramid. Scott greets the group, and Brandon. He then turns to Ash, saying that it looks like this will be his last Frontier Challenge. The King snaps back, saying he does not know about such nonsense. Scott is confused, especially when Ash walks past him and pushes him out of the way. Scott asks what is going on, and May explains that Ash isn't really himself right now. Inside the Pyramid, May explains further, and Scott is shocked to hear that Ash has somehow been possessed by the corrupt ruler of the ancient Pokelantis. Brandon's referee, and the judge of the Pokemon battle about to happen, announces the official rules for the battle, and formally introduces the two trainers. However, when he introduces Ash, The King snaps at him and says once again that he isn't Ash, instead he is the Great King of Pokelantis. The judge is taken aback, but continues his referee announcement, and introduces Brandon, te King of the Battle Pyramid. The battle will be One on One, with no time limit. At that, Brandon sends out Regirock. The King grits his teeth, wondering how he can get through this battle... after all, he has no idea about Ash's Pokemon and strengths. Inside the mind of Ash's body, Ash's coinciousness awakens for the battle- as The King needs him. Seeing Regirock through his eyes, Ash decides that Sceptile would be the best choice for the battle.

The King hears his thoughts, and calls out Sceptile from his Pokeball. The referee starts the battle, and The King, following the thoughts of Ash, calls for a Leaf Blade. Brandon tells Regirock to protect itself, and the Leaf Blade fails to do any damage against Regirock's hardened defence. The King grumbles that Brandon is trying to hide, and orders Sceptile to use Bullet Seed. Regirock defends itself again, and Sceptile attack once again fails. The King curses, before looking up towards the roof and seeing a chance to gain an advantage. The King orders Sceptile o use Bullet Seed on the roof, which causes Sceptile and the group watching the battle to look at Ash in shock. The King repeats his order to Sceptile, who has no choice but to do so. Sceptile fires off a Bullet Seed, which hits the ceiling of the room and sends several large rocks and boulders falling from above and straight on Regirock. Brandon doesn't appear worried, but The King laughs, thinking he has the battle in the bag. Brandon points at The King, and says that such a move was something the real Ash would never do. He continues to speak to him, and it appears that his words seem to be getting through to Ash as the darkness of The King vanishes for a moment.

However, just as everyone is about to welcome the real Ash back, The King resumes his control over Ash. He laughs, and says that it'll take a lot more than that to defeat him. Max is worried, and remarks that Regirock still hasn't come out yet... however, Scott reassures him and says that he need not worry. Brandon and Regirock have gone throughtougher situations than this and still come out on top. Regirock then bursts out from beneath the rocks, and Brandon orders his Pokemon to use Hyper Beam. The King curses, and then orders Sceptile to grab the referee and use it as a shield. Sceptile is shocked, but when The King snaps at it and tells it to do as its told, Sceptile does so and Regirock stops its attack. Seeing his chance to attack, The King orders Sceptile to use Leaf Blade on Regirock, which it does, sending Regirock to the ground... but also seeming to hit a weak spot on the rock Pokemon. Brandon orders his Pokemon to focus and use Lock-On. The King then calls for another Leaf Blade, which again hits Regirock dead-on. Brandon then orders Regirock to use Hyper Beam, and The King laughs, saying that Regirock is too slow to hit Sceptile. He then orders Sceptile to dodge, but after using Lock-On, the Hyper Beam circles around and hits Sceptile square in the back. The force of the attack sends Sceptile falling to the ground and out for the coun, as the referee announces that Sceptile is unable to battle and that Brandon is the winner. The King shouts at the judge, saying that he's wrong and should take it back. He then turns around and says that now Pikachu will battle in Sceptile's place. Pikachu looks worried, but May, Max and Brock all run in front of Pikachu in order to protect it. The King ignores their requests to stop, and orders Pikachu to use Thunderbolt on them. Pikachu struggles to decide what to do... after all, deep down, Ash is still Pikachu's best friend and master. Inside Ash's mind, the real Ash wonders what is going on as everyone is shouting his name. He then sees Pikachu, and realises what to do. Using his own voice, he orders Pikachu to use Thunderbolt on him. Pikachu does so, and the shock of the attack forces the darkness of The King out of Ash and floating in the air. Seeing his chance, Brandon pulls out the ancient Pokeball and sucks The King back inside so he can no long do any harm. With Ash back to normal, May Max and Brock welcome him back and say how relived they are to see that he's okay again.

Meanwhile, Team Rocket are still searching through the underground passages, trying to find some sort of treasure. They then come across a room with a Hoot-Hoot inside. Jessie is annoyed that once again all they've found is useless Pokemon, and throws a rock at the bird. This angers it, and they are once again chased away while being pecked. Jessie steps on a trap tile, which causes the floor beneath them to spring up and send them blasting off.

Back with Ash and co., Ash is thanking May, Max and Brock for everything they did to help him while he was possessed. Brandon then tells Ash that if he wishes to face him again, he will have to train a lot harder, and dedicate himself even more to his Pokemon. Ash begs for another chance, but just as Brandon is about to reply, his judge appears and asks him to come with him to finish off the moving preperations. Brandon then explains that the next time they meet, it'll be in a different location. At that, he walks back into his Pyramid as several large propellers appear from the sides and begin to fly it away. Scott says that this is usual for Brandon, who at heart is an explorer. The group continue to watch the Pyramid fly off, before May notices something else in the sky... a large glowing bird. Ash mutters 'Ho-oh' under his breath as once again he's sent out on another journey and another challenge.

The episode ends with the group's spirits renewed, as their respective challenges come to light and a new road appears in front of them.

Thanks to Alfonso for writing this for us