To Joey's shock, the tournament champion is Mai Valentine! The Big Five approached her to test the game, probably to see if it'd work on Kaiba, and she's not happy to hear they may all be in danger. Using Mai's Harpie Lady to snag the Niwatori card, the group escapes the angry monsters and heads for the desert. Riding their Niwatori across the winds, they make their way to an elaborate maze, guarded by Labyrinth Tanks and other monsters.
Meanwhile, Seto Kaiba regains consciousness. He's been chained to a pillar and guarded by a Witty Phantom, whose voice and mannerisms closely resemble Pegasus. The Phantom tells Kaiba that he, along with another offering, will be sacrificed to bring forth the Mythic Dragon, an unstoppable beast of destruction.
Back in the maze, Yugi and friends defeat Gate Guardian and run into Princess Adena, who closely resembles Mokuba. She thanks the brave heroes for saving her and takes them to her castle. Every year, offerings are collected from Sim Lau and another kingdom to revive the Mythic Dragon. The other kingdom chose Seto for this year's tribute, while Adena volunteered herself to spare her people.
However, there is a myth that legendary heroes will save the kingdoms and destroy the dragon. Yugi and his group are convinced that they are the ones to answer this challenge. To stop the dragon's revival ritual, they must reach the Castle of Dark Illusions, which is in the sky and surrounded by a barrier that no duel monster can pierce. Just then, a swarm of Duel Monsters attack the palace. Adena is seemingly kidnapped—until she reveals that she and Mokuba switched outfits, so he would be taken to Seto. It's more vital than ever that they reach the castle!
Yugi finds the ancient flying machine, but it has long since been corroded and buried. Joey uses Time Wizard to turn the machine's time backwards, restoring the machine. Back in the real world, Tristan and Tea are in a tight spot, doing their best to keep Kemo from breaking into the room and unplugging their pods.
This episode contains examples of:
- Body Double: Mokuba and Adena switched clothes so he'd be captured in her place.
- Continuity Nod: Mai using not only Harpie Lady but also Rose Whip and Mirror Wall is what alerts Joey as to who she is.
- Freeze-Frame Bonus: When the camera is sweeping over the group when the Castle has just shown up, pausing it as Mokuba and Adena are onscreen makes it possible to tell from their different eye shapes and slightly different skin tones that the two have switched places.
- Stating the Simple Solution: Defied twice. Mai first suggests flying to the castle on Joey's Red-Eyes but Adena explains that the barrier prevents this. Then, when the group is attacked by a swarm of monsters, Yugi tries to destroy them all with Dark Hole but an Armed Ninja destroys it before he can activate it.
- Vocal Evolution: Harpie Lady sounds more like an actual girl in this episode.
