After making it to Mauville City, Ash and the gang see a sign stating that whoever can make it through the trick house will win a lifetime supply of PokéBlocks. Ash and the gang decide to try their luck.
When they arrive, they have three doors to choose from. Ash, May, and their new friend Alanna choose one door while Max and Brock choose another. Team Rocket is, of course, also trying to win and each one of them chooses a different door. Everyone ends up trying to navigate through a maze. James and Meowth meet and then see Ash, May, Alanna, and Alanna's Whismur and decide that they want to steal the Whismur. They are successful until everyone exits the maze at the same time and Alanna rushes up to Team Rocket and takes her Whismur back, thanking them for finding it.
Team Rocket creates havoc for our heroes throughout the next few challenges and finally traps Pikachu and Whismur during the last challenge. A battle ensues and Team Rocket is sent blasting off. Ash and company may not have won the lifetime supply of PokéBlocks, but they did make some new friends and are ready to set off for the Mauville Gym.
After arriving at Mauville City, Ash and his friends see a poster advertising a Trick House contest in which the winner would walk away with a year's supply of free Pokéblock. Team Rocket and a wild Jigglypuff also see these posters. Deciding to enter, the group heads over to the Trick House, where dozens of other interested competitors are already assembled. Suddenly, a Whismur pushes Max down from behind, closely followed by its Trainer, a young girl named Alanna. She introduces herself and tells the gang that the famous "King of Tricks" is about to appear. As if on cue, the Trick Master appears, explaining that the Trick House he built will require both skill and wit to pass through, and that only the best would receive the prize. After telling everyone to choose any beginning door they want from the possibilities, he disappears with a maniacal laugh. Max and Brock go one way, while Ash, Alanna and May go another. Jigglypuff spots Alanna and follows closely behind unnoticed. Team Rocket change into school uniforms and split up, with James and Meowth going one way while Jessie heads another.
The first room everyone comes to turns out to be a tricky maze; everyone seems to be getting stuck at dead ends around every turn. James and Meowth happen to spot Alanna's Whismur and plot to capture it, taking the opportunity to abduct it while Alanna's back is turned. Before the confused young Trainer can begin the search for her Whismur, Jigglypuff appears, putting the group to sleep with its Sing. As soon as it's finished drawing in black marker all over their faces in anger, it leaves the scene to continue on through the Trick House. Jessie, James and Meowth meet back up and, with Whismur still in hand, proceed to try to navigate the maze while avoiding Ash and his group, who also met back up with Brock and Max. However, both groups make it out at near the same point and Alanna spots her Whismur, thanking Team Rocket for finding it before snatching it up and cuddling it in her arms. At this point, Jigglypuff appears again, putting everyone to sleep except Whismur who stays awake due to its Soundproof Ability. Jigglypuff is ecstatic to finally find someone who can listen to its singing and it dances around with Whismur in celebration.
Alana and the group wipe their faces clean before proceeding to the next stage, a room with a raging waterfall and wide logs to provide a crossing point over the canyon. Ash is hesitant, but leads the others across a sturdy-looking log. Just before they reach the other side, Jessie rolls their log, knocking them into the water before sprinting across another log and into the next room with her two companions. In the next room, several ropes attached to the ceiling hang over a gap filled with water. Team Rocket swings across easily, but when Ash and everyone else try to cross, they're knocked off by the villains. The next room has numerous boxes nailed to the ceiling with ropes attached. Upon opening a box, one may find either the passageway to the next room, or a toy hammer that delivers a smack to the noggin. As Ash and his friends find one of the few possible correct boxes, James pops out and cuts the rope, causing the twerps to crash to the floor. The next area gives everyone lots of trouble; a large room full of hidden pitfalls. After much trial and error, both Team Rocket and Ash's group make it through to the final stage.
Within the last room, Team Rocket awaits in disguise with different costumes, swinging a gigantic jump rope. They state that all Ash and friends have to do is jump ten times successfully, and they win. The group does so, only to be tied up and have Pikachu and Whismur stolen and stuffed in a bag. Team Rocket then reveals their identities. While they're busy boasting about their victory, Ash manages to get a hand out from under the ropes to call out Corphish, who cuts them free. Jessie and James promptly send out their Pokémon. Cacnea leads off with a Pin Missile at Corphish, which is brushed aside as the Ruffian Pokémon counters with Harden. Cacnea is then sent flying backwards and into Meowth as Corphish strikes back with a powerful Crabhammer. Whismur and Pikachu burst from the bag, running back to their respective Trainers. Enraged, Alanna sends her Whismur after Seviper, knocking it out with a deafening combination of Screech, Supersonic and Hyper Voice. Corphish finishes up with Crabhammer, sending Team Rocket spiraling through the roof of the Trick House and blasting off.
Later, the King of Tricks presents Ivan, a young boy from Mauville City, with the winning prize. May turns to Alanna, admitting that she may have won if Team Rocket hadn’t messed up her chances. However, Alanna declares that she is happy all the same because she got to spend time and battle together with her Whismur. Unexpectedly, Jigglypuff takes to the stage and performs for the crowd. It stops its performance when it sees that the crowd have fallen asleep. This time even Whismur is in a slumber, though not because of Jigglypuff, but because it was exhausted from its adventures through the Trick House. In revenge, Jigglypuff scribbles on everyone’s faces with its marker before storming off.