A girl in a magical world bets her family's magic that nothing bad will happen when kids from Halloweentown attend high school in the mortal realm.
Marnie and her friends from Halloweentown are back in this made-for-cable feature. Marnie is a teenage witch living with her family of supernatural beings in the village of Halloweentown. Marnie and her pals are interested in attending high school in the nearby mortal community, where they'll be able to spend more time with kids their age, and with the help of her grandmother Aggie, she's able to convince the town council to go along with the suggestion. However, there's a catch -- if anything dangerous happens as a result of their presence in the mortal school, Marnie and her friends will lose their magical talents. Trouble does make its way to the school, but not in a way anyone expected -- the Knight of the Iron Dagger comes to the mortal world determined to wipe out Marnie and her magical companions.—Anonymous
Marnie Piper prepares to begin a new school year in her new home. She asks the Halloweentown Witches' Council to work toward openness between Halloweentown and the mortal world. She proposes to bring a group of Halloweentown students to her own high school in the mortal world.—Anonymous
One year after the events of the previous film, Marnie Piper is preparing to start a new school year. She approaches the Halloweentown Council with a proposal to improve relations between Halloweentown and the mortal world by bringing a group of Halloweentown students to her high school. The council is initially hesitant, primarily due to the legend of the Knights of the Iron Dagger, a fanatical group that sought to eliminate all things magical. Ultimately, however, the Halloweentown Council agrees to Marnie's plan after she mistakenly wagers "all the Cromwell magic" that her idea will succeed. If she fails to prove her point by midnight on Halloween, her entire family will lose their magical abilities. Regretting her impulsive bet, Marnie wishes to cancel the exchange program, but her grandmother, Aggie, encourages her to go ahead, asserting that they have nothing to fear.
When the Halloweentown students arrive, they are magically disguised to appear human. Marnie acts as a tour guide for the group, telling others that they are from Canada. Aggie substitutes as a teacher to be available for any issues that may arise. Meanwhile, a new student named Cody shows romantic interest in Marnie.
Although Aggie struggles to effectively teach, the Halloweentown students initially keep to themselves, taking refuge in a magical hideaway created by Aggie in a remote locker. Marnie gradually encourages the students to participate in sports, school activities, and to make friends.
Marnie's efforts are interrupted when she receives a warning that seems to be from the Knights of the Iron Dagger, followed by a magical incident at the mall where the Halloweentown students accidentally reveal their true forms to the public. This is compounded by a break-in at their secret locker and the mysterious disappearance of a student named Cassie.
At the same time, Marnie's relationship with Cody develops alongside an unexpected romance between Aggie and the school's principal, Phil Flanagan. Aggie suspects Cody of causing problems and tries to persuade Marnie to end their relationship, while Marnie begins to suspect Flanagan. Eventually, they discover that Flanagan is, in fact, a member of the Knights; he was informed before the students' arrival that he was the last remaining knight of the Order.
The real antagonist, Edgar Dalloway, the head of the Witches' Council and father of one of the students, is the source of their troubles. He wants to keep Halloweentown isolated from the mortal world and has manipulated Flanagan to ensure Marnie's project fails. Dalloway hoped that this failure would provoke a negative reaction in Halloweentown, keeping the portal between the two worlds closed.
During the school's Halloween carnival, the Halloweentown students aim to improve mortal perceptions of magical beings. Their haunted house showcases the everyday lives of creatures typically viewed as monsters by mortals, featuring displays such as a "Monster Tea Party" and ogres "picnicking in their natural setting," which ultimately fails to engage the carnival-goers. Meanwhile, Marnie's mother, Gwen, uses a Witch's Glass to search for Cassie.
At the carnival, Dalloway unleashes magical attacks on the mortal students by animating the inanimate monsters from the haunted house. Panic ensues, spiraling out of Marnie's and Aggie's control. Flanagan incites a mob against the Halloweentown students. However, Cody calms the crowd, leading the students to reveal their true identities. The crowd eventually accepts them for who they are, and Flanagan renounces his status as a knight to embrace Aggie.
Dalloway claims the Cromwell magic for himself and reveals that his son, Ethan, was complicit in many of the recent incidents. However, Gwen presents the evening's events to the Halloweentown High Council, leading them to restore the Cromwell magic. Gwen returns with the rescued Cassie, while the Council imprisons Dalloway in another Witch's Glass, interpreting his disagreement as a resignation and stripping his family of their magic.
As a result, the portal between Halloweentown and the mortal world opens within the haunted house, allowing countless children from Halloweentown to cross over and enjoy the carnival alongside their mortal counterparts. Marnie then flies off for a romantic broom ride with Cody, and as they soar over the carnival, they share a kiss.
