Mallow notices Lana's glumness and asks about it. Lana admits that her twin sisters, Harper and Sarah, have spoken nonstop about going to a haunted house. The class are intrigued by the idea, just as Popplio spots Mimikins and Acerola through a doorway. Ash officially introduces Acerola, who reveals she decided to stop by while she delivered a book from the Malie Library. Lillie notices Mimikins's strange floating and peculiar color, which Acerola explains is because her Mimikyu is an actual ghost. Ash asks Acerola if she knows of any haunted houses; she denies it but suggests the group just make their own instead, something Principal Oak agrees with.
Ash and his friends spend the afternoon setting up the haunted house attraction. The night settles in, and Principal Oak remains on campus to assist the students if needed. Meanwhile Lana has brought Harper and Sarah along to enjoy the haunted house experience, with Rotom as their guide. Ash and his friends rush inside to fulfill the twins' expectations. Sophocles watches from the surveillance as Rotom and the twins make their way through a hallway. At his command, Mallow creates a fog to give the area an eerie feel while Lillie controls a Pyukumuku on a line to imitate a ghost. Unfortunately the twins are unfazed by the supposed ghost and go on to touch Pyukumuku who then punches Rotom. As the twins make their way down a fleet of stairs, four ghosts appear, which are actually Ash, Kiawe, Pikachu, and Marowak in disguise. Harper and Sarah scream in enjoyment as the quartet of ghosts chase after them. The pursuit soon ends after Ash steps on Pikachu's tail causing him to unleash a Thunderbolt on everyone.
Suddenly, things begin to float mysteriously and everyone rushes to the classroom where Ash and Kiawe are standing. Acerola has her Shuppet use Foresight on the strange phenomena, which reveals that a group of Ghost Pokémon are behind the mayhem. Ash thanks Acerola, and she admits that Ghost Pokémon tend to follow her around likely because of Mimikins being a ghost. The twins are ecstatic and rush to play with the Ghost-types. Haunter licks the twins' faces and a Phantump plays a game of peek-a-boo with them. Everyone is glad to see the twins are having fun, but Acerola warns that Ghost-types have a habit of carrying people they like away. Realizing the potential dangers, Lana attempts to call her sisters back but they ignore her pleas. Mismagius appears in front of Lana and unleashes a wave of energy that transports Ash and his friends to a strange graveyard world.
Upon arrival, Mismagius carries the carefree twins away while a group of Gourgeist blocks anyone from intervening. Pikachu uses Thunderbolt on the Gourgeist, and the wild Pokémon return to being pumpkins. Following Acerola's suggestion, Mimikins leads the group to a nearby mausoleum. As Ash and his friends make their way down, the stairs crumble under their feet and they drop down into another area. Lana soon spots her sisters who are enjoying soaring through the sky with their Ghost-type friends and their new sets of Vivillon and Beautifly wings. Lana's stern commands are once again ignored, and Mismagius warps everyone into another illusion.
Mallow and Sophocles find themselves in a purple forest and soon discover a house made of sweets. The pair and their Pokémon enjoy a bite of the cottage's outer walls. Before too long, they have gorged on most of the house and have become too fat and swollen to move. Elsewhere, Ash, Lillie, Kiawe, Rotom, and their Pokémon stop in a forested area to watch a Banette perform a marionette puppet show. Ash, Kiawe, and Lillie soon find themselves immobile and then realize that they have become marionette puppets themselves.
Lana and Acerola have a tea party that quickly escalates into a dangerous situation. The pair and their Pokémon board a giant tea cup as Chandelure continues to pour a great flood of tea. Lana is able to row the cup away from Chandelure with a giant spoon, and later uses one of Popplio's water balloons to rescue everyone from going over a waterfall. As the giant bubble continues to float higher into the sky Acerola questions whether anything is real or is the world just one of Mismagius's illusions. Lana considers the possibility and notes that they would just need to wake up if it were just an illusion and smacks herself in the face, but instead, she ends up with pained and comically swollen, red cheeks. A giant Komala spares Lana and Acerola from an angry group of Drifloon and Drifblim. After Lana's desperate pleas, a giant school bell appears in the sky and Komala rings it loud and clear. Its tolling captivates everyone's attention, and they soon wake up in one of the Pokémon School's classrooms.
Principal Oak finds his Komala sleeping by the school's bell, and questions why it rang the bell at such an odd time. Meanwhile, Acerola and Lana inform Ash and the others that they were caught in a dream created by Mismagius. Everyone is thankful for Komala's efforts, but Acerola apologizes for embroiling everyone in the chaos. Lana points the finger at her two sisters, but the twins remain unaware of the concern they caused and simply want to have more fun with the Ghost Pokémon, much to the disbelief of Ash and his friends. Then, Lana finally loses her patience as an ominous aura envelops her. She stomps her foot on the floor and calls out to Harper and Sarah, who promptly get terrified by their big sister's ominous appearance. Afterwards, Ash and his friends start cleaning the school while Harper and Sarah remain frightened and comment that Lana is scarier than the haunted house.