When a young girl living with her secret witch mother learns she too is a witch, she must help her witch grandmother save Halloweentown from evil forces.
Marnie, Dylan, and Sophie Piper have their first out of many adventures! On Halloween, while Marnie is arguing with her mother Gwen, the kids' grandmother Aggie comes to visit. Aggie wants to start Marnie's witch training before her 13th birthday or Marnie will lose her powers forever. But there is another reason for Aggie's visit. Something dark & evil is growing in Halloweentown & Aggie wants help to defeat it. While Aggie & Gwen are arguing, Aggie uses magic which Marnie observes. After Aggie leaves to return to Halloweentown, Marnie, Dylan and, unknown to Marnie and Dylan, Sophie follow her onto the return bus. Soon afterwards, Gwen follows the children to Halloweentown. While there, Aggie & Gwen are attacked by the dark force in a movie theater. Marnie, Dylan & Sophie race to get the ingredients to activate Merlin's Wand to stop the evil.—LepricahnsGold & Corey Semple <Superman2002>
Gwen Piper, a widowed mother, always refuses to let her children-Marnie, Dylan, and Sophie-go out on Halloween. Each year, her mother, Aggie, visits for the holiday, bringing excitement to the children, much to Gwen's dismay. While Aggie openly encourages the kids to embrace Halloween, Gwen is frustrated, determined to raise them as mortals, just like their father.
During her visit, Aggie reads the children a bedtime story called "Halloweentown," which describes a mystical place where witches, vampires, and monsters coexist peacefully, away from mortals. Sophie points out a drawing of a witch resembling Marnie, and Aggie encourages Marnie's imagination without objection. After saying goodnight to the children, Gwen and Aggie argue. Marnie, eavesdropping, hears Gwen express her anger at Aggie for promoting Halloween fun and insisting that Marnie be raised as a mortal. Aggie, however, wants to train Marnie before she turns 13, as without training, Marnie risks losing her powers. Aggie also reveals her concern that citizens of Halloweentown have been disappearing, although Gwen suggests they may have simply moved.
When Aggie leaves to return home, Marnie and Dylan secretly follow her, only to find out that Aggie boards a magical bus to Halloweentown. To their surprise, Sophie has sneaked onto the bus with them. The trio quickly begins searching for Aggie and is approached by Kalabar, the mayor of Halloweentown, who arranges for them to take a cab driven by Benny, a humorous skeleton. Benny drives the children to their grandmother's mansion.
Aggie decides not to send them home right away. She promises to start Marnie's witch training but is first focused on a mysterious threat, described as "the bad thing." Using her cauldron, she sees a vision of a hooded figure laughing maniacally. Aggie explains she must activate Merlin's talisman with a spell and a potion to confront the evil creature.
When she fails to light the talisman using an "instant" potion, Aggie takes the children into town to gather ingredients. They encounter Luke, a goblin who was transformed into a handsome human by a shadow creature; he awkwardly flirts with Marnie, but she declines his advances. Meanwhile, Gwen arrives in Halloweentown in search of her children, but upon realizing they are there, Marnie objects to returning home. Unable to find a bus back to the mortal world, Dylan suggests they see the mayor for help. To Gwen's shock, the mayor is Kalabar, who turns out to be an ex-boyfriend of hers.
Kalabar leaves momentarily to address another matter but promises to assist them upon his return. In the meantime, Aggie meets up with Luke, who informs her that the evil creature is after Merlin's talisman and leads her to him. Gwen and her children spot Aggie and Luke walking together and suspect Aggie might be in danger, prompting them to follow.
In an abandoned movie theater, Aggie discovers that some Halloweentown citizens have been frozen in time and encounters the hooded demon on the screen. She refuses to hand over the talisman. Gwen and the children enter just as Luke runs out in fear. The demon freezes both Gwen and Aggie, and the children escape to gather the ingredients needed-a werewolf's hair, a ghost's sweat, and a vampire's fang-to create the potion that will activate the talisman and free the others.
They realize they must place the talisman inside a large jack-o'-lantern at the center of the town to defeat the demon. When they arrive, the demon reveals himself to be Kalabar, attempting to persuade the townspeople to join him in taking over the mortal world. With Luke's assistance, Marnie climbs onto the jack-o'-lantern and attempts to place the talisman inside, but Kalabar casts a spell to freeze her. As she begins to lose consciousness, Marnie drops the talisman into the jack-o'-lantern, causing it to glow brightly. This act unfreezes her and everyone trapped in the theater, and it weakens Kalabar.
The children reunite with their mother and grandmother, learning of Kalabar's true identity. He reveals his bitterness over Gwen choosing to marry a human instead of him. Kalabar seizes the talisman, declaring he will use it to rule both the mortal and magical realms. Dylan reveals he has acquired magic powers as well, and he joins forces with Gwen, Aggie, and his sisters to defeat Kalabar. In the end, Kalabar is vanquished, and Aggie retrieves the talisman. Luke is turned back into a goblin but receives a kiss on the cheek from Marnie.
Deciding to stay in the mortal world to spend more time with her grandchildren, Aggie collaborates with Gwen to train Marnie as a witch. They board the bus together, setting off back into the mortal world.
