Plot

A young girl tries to fit in with a clique of popular middle school girls after moving into the guest house of one of their homes.

Massie Block is the leader of a small group of privileged schoolgirls who arrogantly call themselves 'The Pretty Committee'. These so-called pre-teen 'mean girls' (cynical, egotistical, selfish and narcissistic females) and their clique are respected and feared in their middle school as well as their upper class Rhode Island suburban neighborhood. But Massie's life takes an unexpected turn when her parents friends, a lower-middle class family with a self-assured daughter named Claire move into the Block's guest house and Claire threatens to undermine the superficial Massie's position of the clique.—matt-282

Massie Block is a cynical 13-year-old 'mean girl' who is first seen screaming in her bedroom at her parents. She was going to a party but Massie's parents, Kendra and William, will not let her go because William's friend, Jay, and his family are moving to the small Rhode Island town of Westchester where they live from Orlando, Florida to stay in their guesthouse. Massie is angry with them so she calls her friends; Dylan, Alicia, and Kristen, who form a local clique called 'The Pretty Committee' to spread the word about the new people in town. Massie tells them that the host of the party, Shelby Wexler, has head lice, so that Dylan, Alicia, and Kristen will not want to attend.

Massie goes to the house's indoor swimming pool and is reading a magazine when her mother comes out to make a deal with her. She says that she can go to the end of the party if she will be nice to Jay's daughter, Claire, a girl who is Massie's age, and will be going to her school, Octavian Country Day.

The next scene shows Claire and her family arriving at Massie's house. When Massie first sees Claire, she hates her right away, judging by her outfit which is a typical design not an expensive and imported item. Todd, Claire's 10-year-old brother, is shown to have an obvious crush on Massie.

At dinner, Claire gives Massie a charm of a silver microphone for Massie's charm bracelet which Massie makes a rude comment about. Massie then tries to leave for her party but is overheard by Claire, whom Kendra invites to go to the party, but Massie, not wanting to bring her, fakes sick. Claire, envious of Massie's colorful fashion and clothes, asks her mother to take her shopping for new clothes for school. After some begging, her mother agrees.

At the mall, Claire meets one of the mean girls, Dylan, who is in a fight with her own mother because she refuses to buy Dylan pants as she is not a specific size. Claire tells Dylan to switch the tags, which Dylan delightfully replies saying, "You're a brilliant!" Once seeing the rest of her friends, she leaves thanking Claire, who, turning away, smiles.

The next day, Massie decides to go riding with her horse, Brownie. On her trail she meets a boy named Chris Abeley who Massie instantly develops a crush on. After a short conversation, they make plans to go riding the following week, in which Chris says "It's a date."

The following day, Claire hears she is going to school with Massie, much to her excitement. She gets into the car, soon to be accompanied by Massie, who requests that she sits in the back, as they have to "pick up a few more" (Dylan, Alicia, and Kristen). Dylan and Claire recognize each other, and Dylan immediately then stops liking Claire because of Massie's disapproval. During the ride, Kristen asks Massie if they "like" Claire, which Massie coldly replies "No." When Claire is walking to school, she runs into Chris Abeley, who is riding his skateboard and trips, falling onto Claire. Seeing him, Claire develops a crush on him. Massie sees this and storms into the school, furious. Claire comes by and asks Massie for a room location, which Massie replies Claire to "go back to wherever the hell you came from", then offers her friends lattes. When Claire insults Massie by calling her a "bitch" right to her face, Massie vows revenge for this.

Claire goes to art class where the class is supposed to paint a still life of tomatoes. Alicia, who was next to her, delibirately spils red paint on Claire's white jeans, then IMed her friends that she got her period. The art teacher, Vincent, tells Claire to go to the nurse. Claire, not knowing why, asks Dylan for directions, in which Dylan gives Claire the false directions to the class Massie is in. Claire then finds the real nurse's office, and gets new clothes from her "period". At lunch, Massie's crew makes fun of her and laughs at her outfit, causing Claire to leave. Massie, Dylan, Alicia and Kristen have afterschool plans as well, to watch Chris Abeley at school, and Claire is not invited, so she walks home.

The next day, when Claire is at school, she decides to make a new friend and show Massie up. She befriends Layne Abeley, who is Chris's little sister. Claire tells Layne she is friends with Massie, lying that she is jealous that she has a new friend and can't only hang out with her. Layne and Claire decide to hang out on Friday, but when Claire comes back home Kendra told Claire that every Friday Massie has a sleepover with her friends and invites her as well. Claire accepts, but she does not know that Massie doesn't want her to come.

Claire calls Layne and lies that she has to babysit for Todd, and goes to the sleepover. They are donating old clothes for the annual auction, and they all look at her like she doesn't belong there. Massie and her mother talk, and Massie's mother tells Massie that she has to be nice to Claire. Massie invites Claire to the place they go to sleep during the sleepovers, so Claire goes down. The girls were playing What Would You Rather? Alicia asks if they would rather be A): Friendless losers or B): someone with a ton of friends who secretly hate them. Claire picks A, which Alicia says, "Congratulations, you got your wish." Claire turns to go, but Massie says, "Have you ever played truth or dare?" so they start to play. They then go to sleep, but Alicia makes a farting noise and asks Claire if it was her. Claire gets up to leave, Massie tells her she doesn't have to go. Claire says she wants to.

The next day in the car, Kristen tells the girls she has to do a project, so the girls decided to make a make-up company which Claire named Glambition. When the girls go to make their Glambition lip gloss, Dylan, Alicia and Kristen are waiting for Massie, but Claire wanted to go for a swim. Massie is out riding with Chris Abeley and finds out that Layne is Chris's sister, therefore pretends to be friends with her. Claire convinces the three to swim with her, and they all have fun. Claire lies about the brand of her bathing suit, telling them it is an original Astrud but when Massie comes back from seeing Chris Abeley, she sees through Claire's lie and calls her bathing suit a knockoff.

Claire goes home in tears. Her mother sees that something is wrong, telling her to talk to Massie. Claire goes up to talk to Massie about what happened, but it turns out Massie is not there, so she sneaks over to her iMac computer and pretends to be Massie while IMing Alicia, telling her that she likes Claire now and that she is wearing shorts over tights the next day, which everyone but Massie wears.

The next night, Claire goes up to Massie's computer again, and insults Dylan's legs, asking if she thinks her legs look good in in a miniskirt, causing Dylan to be mad at Massie and it leads to Dylan only wearing only long skirts the next day to hide her legs.

The next night, Claire kidnaps Massie's dog Bean to send Massie to go look for Bean. Claire sneaks into Massie's room again and IMs Kristen, tricking her into telling that she's poor. She escapes in time to get away from Massie.

The next day, Kristen, Dylan and Alicia befriend Claire and dethrown Massie, because they believe that she is friends with Layne instead of them now, and make Claire their leader. Claire accepts, and even hangs out with them after school. They go to a designer store, and Alicia offers to buy her a dress and gives Claire her old cell phone. They then go back to Dylan's house and have fun trying things on and messing around. Claire goes home and starts talking back to her mother, being more like Massie was as her new status as the Queen Bee of the Pretty Committee is getting to her.

That night, the alone and behwildered Massie IMs all of her friends, but only Kristen replies because Massie tells her that she has the makeup lip gloss tubes, and Kristen comes to pick them up, which the two of them get into a screaming argument and Massie figures out about Claire using her IM while she was out to bad-mouth her to her minions of the clique.

Massie calls Claire with her other friends on a five way conversation, and tells her that her fun is over, exposing Claire as the one responsible for their internal feud, then hanging up on her.

Restored as the leader of the Pretty Committee, Massie now embarks on a hell-bent mission to destroy Claire's life for her deception and attempts to take her on. The girls come over to Massie's house the next day to mix the makeup recipe together to hand out at the school field trip. The girls gossip about Chris Abeley, and Massie asks her friends what to do for Chris Abeley's birthday. They plan for Massie to jump out of a cake at the auction. Claire then comes down and asks to borrow an egg, which Massie agrees to, throwing it at Claire, who runs upstairs crying.

Claire confides in her mother about things she did and what's going on, and the next day at the school field trip, Claire makes up with Layne. When the Pretty Committee starts selling their lip gloss, all the girls lips swell or burn from alergic reactions to the experimental solution, which Claire saves the day with oatmeal, to help the girls' lips. While Dylan, Alicia, and Kirsten half-heartedly thank Claire for saving their reputation, Massie does not, fearing it will weaken her hold of power as Queen Bee.

The next day at the auction, Claire meets Chris Abeley's girlfriend, Fawn, and Claire saves Massie from an embarrassing situation by sitting on the cake and asking Fawn to come up and talk about Chris. Massie and Claire talk backstage from the stage, and Massie is nicer and gives Claire a flower.

In the final scene, Claire goes to bed and tells her mother that Massie gave her the flower and she wants Massie being nice to her as well as the flower to last for a long while. In Massie's room, she makes a list of the pros and cons of her life. Massie lists Claire's name in both the pro and con list implying hope that Massie might let Claire become a member of the Pretty Committee that she continues to hold an iron grip over.