After making it out of Petalburg Woods, the group finds themselves in the urban center of Rinshin Town. May is keen to do some window shopping, Ash wants to get something to eat, Brock needs to stock up on supplies and Max is all for Pokémon hunting. The group decides to split up for the afternoon - May and Brock will go to the shops while Ash and Max find somewhere to eat. Meanwhile, Team Rocket are working as manual laborers on a building site in the city, tearing down an old, disused mansion. The other workers are worried by what seems to be ghosts in the mansion. May drags Brock off to look at fashion and accessories. He's extremely bored. He would rather be buying medicine and ingredients for Pokémon food, but May says that can wait. Eventually, he gets his stuff and they're walking through the streets when they hear a woman mention a curse. May is instantly interested and eager to hear the tale of a haunted mansion. The woman explains that the property is known as the Green Lodge, and demolition workers have been quitting because of strange happenings. Brock gets scared, but May insists on going over to check out the haunted house.
After eating a burger, Ash and Max head off to the alleyways in the city, where they peer in looking for Pokémon and spot a Shroomish, who doesn't look too happy. Max wants to feed it and make friends with it, so Ash hands him some Pokémon food. Shroomish is suspicious and uses Stun Spore causing Ash and Max to retreat. Afterwards, Ash takes out some of Brock's Pokémon food, stacks it on a piece of paper and sets it in front of the Shroomish. Shroomish still doesn't want to eat it, until Pikachu jumps down from Ash's shoulder and takes a piece to show that it's safe to eat. Shroomish tries the food and loves it. Ash and Max are surprised because Shroomish is in the city instead of the forest, where it normally would be. They think it might have been separated from its Trainer and maybe they should take it to a Pokémon Center. Max takes out a handkerchief and ties it around the top of Shroomish's head, as a gift. Shroomish is very happy with this. Max picks up Shroomish and they head off.
Brock and May are inspecting the Green Lodge, and Brock comments that they really should let it go. May's still very excited about the prospect of ghosts, so she approaches the manor and Brock reluctantly follows her through the entrance gates. Soon after, Ash and Max stop in front of the manor house after noticing Shroomish staring intently at it. They're spotted by the Rocket trio, and Jessie and James immediately drops the log they're holding to hatch plan to catch Pikachu. Meowth is left holding the log, which quickly drops on top of him. Shroomish, still in Max's arms, gets very distressed and runs off. Ash and Max follow it. Shroomish goes into the mansion through a broken window. Ash and Max follow after Shroomish, but they lose track of and instead find May and Brock standing outside the lodge. A man, Alex approaches the group ordering them to move on because of the demolition works. Max explains that they were just following a Shroomish, but Alex refutes the claim entirely. He informs the group that the Green Lodge belonged to his grandfather, and he used to stay over and play with the resident Shroomish as a child. Alex claims the Shroomish have since disappeared because of Rinshin Town’s growing city blocks and his grandfather's passing. Alex explains that he is simply on site to check on the demolition’s progress, but strange occurrences have been hampering efforts. May is keen to hear more details, but Alex replies that it’s just rumors. Max and Ash again affirm their story, so Alex decides he'll have to go inside and see for himself and the others follow him.
Inside, they find Shroomish shivering by one of the old fireplaces. Max approaches to attend to his friend when two other Shroomish emerge, also looking frightened. Pikachu goes to talk to them, while the humans decide that they must be upset because they'll have no home when the mansion is torn down. Team Rocket arrives by crashing through the floor. After reciting their motto, James and Jessie send out Cacnea and Seviper. As the confrontation is about to begin, the trio of Shroomish let out a cry. A whole herd of Shroomish arrive, quickly filling the room. Seviper knocks some of the Shroomish away with a Poison Tail and Cacnea attempts a Pin Missile attack. The Shroomish are unimpressed and fill the air with a cloud of Stun Spore. Alex leads the group outside for some fresh air, while Team Rocket are left paralyzed by the Stun Spore.
Outside, Alex and the others affirm that the strange footprints and odd occurrence are because of the large number of Shroomish that call the Green Lodge home. Max adds that the Shroomish are in pain, and he informs Alex that the Shroomish want just want to play with him like the old days. Alex admits that he shares their sentiments. Alex formally apologizes to Shroomish, but he admits that the demolition must progress.
Suddenly, Team Rocket arrives on the scene to get their revenge on the Shroomish, this time with a brand new mecha. They begin ramming the lodge's walls, and the commotion leads all of the Shroomish to flee the building. Team rocket then picks up and the Shroomish, tossing them all into the capture net on the back of their vehicle. Ash orders Pikachu to use Thunderbolt, but Team Rocket’s machine is unscathed. The first Shroomish is angry and leads its comrades in a Stun Spore barrage, but since Team Rocket's vehicle is airtight, nothing gets through and that includes fresh air. The Stun Spores go off towards the city, but Brock's Forretress heads it off with a Rapid Spin attack. Jessie and James start feeling weird from lack of oxygen so Meowth opens the windows. While this lets in fresh air, it also allows the Stun Spore into the cabin. As Team Rocket feel the full effects of Stun Spore, Alex orders the Shroomish to attack with Leech Seed, and the vines beginning sapping away the Rocket trio’s energy. May's Torchic burns through Team Rocket's giant basket with its Ember attack to free the other Shroomish. Afterwards Pikachu delivers a detonating Thunder to send Team Rocket blasting off.
Afterwards, Max asks about the fate of the Green Lodge again. Alex affirms that the mansion will still have to be demolished. He adds that he'll replant the whole area full of trees so there will be a forest like there was before, and the Shroomish agree enthusiastically. Ash, May, Brock and Max wave goodbye to Alex and the happy herd of Shroomish.