Double, Double Toil and Trouble
Kelly (Mary-Kate Olsen) and Lynn Farmer's (Ashley Olsen) parents, Don (Eric McCormack) and Christine (Kelli Fox), are deeply in debt and in danger of losing their home. During the Halloween season, they visit Christine's cold and cruel Aunt Agatha (Cloris Leachman) to ask for a loan, which is immediately refused. While the girls wait outside, they meet Agatha's grave digger (Wayne Robson) who tells them the story of Agatha's twin sister Sophia (also played by Cloris Leachman) who is trapped inside the house. He explains to the girls that Agatha’s home once belonged to a powerful witch who, before being burned at the stake 200 years before, had hidden her moonstone, the rare gem which gave her power. As children, Agatha and Sophia, tired of being twins, heard the tale and began looking for the stone in hopes of using its power to no longer be identical anymore. Agatha found the moonstone but hid it from her sister and instead began using the magic it possesses to make her sister’s life miserable. Years later on Halloween, Sophia and her fiancé George, now Agatha's butler, prepared to elope and begin their life together, but Agatha, out of jealously and rage, cast a spell that banished her sister into the netherworld through a mirror, which she keeps hidden in the attic. On the 7th year at midnight, this Halloween, the spell will become permanent and there will be no way for Sophia to be rescued.
Back at home, Kelly and Lynn learn of their parents' financial problems. Christine expresses that if Aunt Sophia were still around, she'd be able to help them. Knowing this, the girls begin a rescue mission to free Aunt Sophia before it's too late. The spell can only be broken by twins who have possession of the moonstone, so Kelly and Lynn’s ultimate goal is to apprehend it. The only problem is, Aunt Agatha wears the gem around her neck at all times. While out trick or treating, they swap costumes with two other kids so they are able to get away from their parents. The first person they meet is a homeless man who dreams of money and stardom, Mr. N (Meshach Taylor), who offers to help the girls because they shouldn't be on such a dangerous journey without an adult. The girls carry with them a toy magic wand that they won at a Halloween party days before, which actually has unexplained genuine magical powers. Kelly, Lynn and Mr. N visit a phony psychic to ask where they are able to find the witches gathering that Aunt Agatha will attend that night, but Lulu is unable to answer, so instead, they use the wand to find the location and set off again by secretly hitching a ride on a pumpkin truck. They get dropped off near a woodland and find a small house deep inside, the home of a man named Oscar (Phil Fondacaro) who wishes to be taller. They tell him the whole story and he agrees to go along with them. Meanwhile, Don and Christine discover the girls have gone and inform the police.
Aunt Agatha overhears the girls' plan using the magic mirror and starts doing anything she can to get rid of them. She is threatened by their presence because she knows that the power of twins combined is superior to her own. Kelly, Lynn, Mr. N and Oscar turn up at the gathering in costumes in hopes of fitting in better and they oversee the events inside. Aunt Agatha reveals the story of her spell on her sister to the crowd while Mr. N and Oscar create a plan to try to get her to hand over the moonstone, which she does, intrigued by their promise to double her power. However, they are soon found out and get chased through town. They decide to split up; Lynn, who has the moonstne, with Oscar, and Kelly goes with Mr. N.
Followed by Agatha and her butler, Kelly and Mr. N run into a dead end at an abandoned warehouse. He goes out to confront her but she turns him into a crow, leaving Kelly alone. Later on, Aunt Sophia appears to Kelly, expressing that Aunt Agatha has freed her, but Kelly realises it's a trick and that Aunt Agatha has transformed herself to try and catch her. She manages to tie Agatha up with the magic wand, which messes with her power, but Kelly then gets caught by George when she flees from the building. Mr. N, as a crow, finds Lynn and Oscar to tell them what's happened, and Lynn starts to panic, since her and Kelly have never been apart and Kelly is probably scared all by herself. In the same part of town, Lynn finds where Mr. Gravedigger lives and goes to ask for his help since he knows his way around Aunt Agatha's house more than any of them. On their way, the police officer looking for the girls sees them driving away. She informs Don and Christine where she saw them, and Christine realises it's near Aunt Agatha's mansion so that's probably where they're heading.
Fifteen minutes to midnight, the group break into the house to search for the mirror. Lynn hears Aunt Sophia crying out for help in the attic and she goes to investigate. The good news is, Lynn has the moonstone, but the bad news is, Kelly isn't there, and she needs both twins to free her. Minutes later, Agatha, George and Kelly arrive, and Agatha attempts to poison them with jealousy and resentment toward one another. She tries to persuade Lynn into betraying her sister, but Lynn refuses, since she's realised Kelly is the most important person in her life. Still, she promises to hand over the moonstone if Agatha lets everyone go, which Agatha agrees to. Lynn places the moonstone on the floor and then Aunt Agatha breaks her end of the promise, threatening to turn everybody into animals forever. Mr. N flies down the staircase and snatches the moonstone away in his beak, while Kelly escapes from George's watch and the girls flee upstairs to free Sophia together. They ask Sophia what the incantation is, but Sophia reveals that it has to come from their hearts.
Aunt Agatha bursts into the room laughing, revealing that it's after midnight. Lynn and Kelly tell each other that they love each other and want to be sisters no matter what anybody else says or thinks; the power of love and loyalty transcends all, and Sophia is finally freed. Lynn explains she pushed the clocks ahead five minutes, so it wasn't too late after all. Enraged, Agatha attempts to push her sister back into the mirror, but the twins fight back and Agatha falls into the mirror herself. All of Agatha's evil magic is undone and the mirror is shattered, thus dooming her to spend the rest of her life in solitude in the netherworld.
Don and Christine arrive at the mansion to find Sophia safe and happily returned. Everyone keeps what happened a secret, preferring to tell them that Agatha went on a long trip to "reflect". Kelly and Lynn thank their new friends for helping them out; Mr. Gravedigger for his courage and bravery when standing up to "you know who", Oscar for his fabulous plans and distractions, and Mr. N for being their first companion who looked out for them on the road. He tells them he's also learnt that money is just money and that friends are more important. Aunt Sophia and George fall in love all over again, and redecorate the mansion so it's a second home for the whole family. She also agrees to give the Farmers the money they need to save their home.
Days later while enjoying family time in the garden, Lynn and Kelly are cleaning up the broken mirror in the attic and they see Aunt Agatha in one of the broken pieces. She asks for help, but the twins say "No chance" and walk out of the attic while holding hands and the magic wand. The movie ends with Aunt Agatha shouting, "I hate Halloween!"
good versus evil, flashback