The movie starts with Mary dancing and singing in her own music video. Then she is rudely awakened from her daydream by Dominique Blatt a used to be pop star shooting a commercial for back acne cream. Turns out Mary was a daughter of a back up dancer for Dominique but died and so Dominique took Mary in to do housework. Dominique also has two daughters who aren't the brightest crayons in the box and torment Mary on a daily basis as does Dominique. Dominque and her daughters drive home in her limo while Mary has to ride her skateboard to their mansion. She lives in the guest house by the garage. As she is folding the laundry she is watching a news report on Joey Parker international pop sensation and teen hottie. The interview reveals that Joey is returning home to Los Angeles/Hollywood to finish his senior year of high school and taking a break from the celebrity life. That is the same high school Mary and the daughters Bree and Britt go to. The report also states that JP or joey parker and his label are sponsoring a dance competition and the winner will dance with him in his next music video. Then Dominique buzzes Mary and yells at her for not tivo-ing her dramas.
The next morning Mary wakes up and is picked up by her best friend Tami in the great pumpkin, Tami's large orange vintage van. They talk about their future, Tami aspires to be a famous designer and Mary wants to go to Manhattan School of Performing Arts to be a dancer. As they drive up to school Mary is doubting her future and her dancing abilities when Natalia, the popular girl in school, drives up in her convertible with Bree and Britt. She talks about some one sip diet and throws her soda at Mary. She makes a mean comment about how Mary was invisible and that she didn't see her there. Tami returns with a rude remark of her own. As they walk into school, a jock makes a comment to them and as usual, Tami returns with another comment and Mary compliments her. Then a cheerleader screams its Joey Parker and mass of students run out to meet Joey as he is getting out of the car with his best friend Dustin. Mary states we should probably go before we get trampled and walks away from the scene. Joey is met with a plethora of people and even a barfing fan. Joey and Dustin are conversing about how Joey just wants to be normal again. Him and Dustin are messing around when Joey runs into Mary causing her to run into other people and drop her books. They lock eyes until Joey is dragged away by Natalia. Dustin and Tami share a moment of their own with some verbal flirtations.
After school, Mary rides to a dance studio and sneaks into a back room that reveals a room that can see into the dance room adjacent to it but on the otherside all you can see is mirrors. There are students stretching as they wait for their dance lesson. Clearly Mary has been taking dance lessons on the other side without anyone suspecting. Natalia goes up to the mirror to apply lipgloss when Bree comments on how hurtful it must be to know Joey is back after he dumped her before he left for his tour. She states they will back together before the black and white ball. They start doing warmups when they are then distracted when JP walks into class and the teacher asks him to teach her dance class. As he is doing the steps the students follow and so does Mary. Clearly Mary has much better dancing skills than anyone in the room. As the scene rolls along, JP lets the class freestyle the dance he taught them and Natalia throws her self on him but JP pushes her off as he continues dancing. As he is dancing on one side of the mirror, Mary is on the other side reflecting his every move, the perfect partner. Then Mary's cellphone goes off as the teacher yells at the students for bringing a cellphone. Mary answers quickly and its Dominique on the other line yelling at her for being late. There is an important luncheon and she wants crab puffs. Mary quickly rushes home to be greeted by her stepsisters. They show her a video Mary made when she was eleven about how much she loves joey parker and he's totally kissable and then she starts dancing, like an eleven year old. Mary is angry they went through her stuff and she tries to take the tape but the sisters state that they made copies. As they are jinxing each other, Mary runs out and makes the crabpuffs.
The next scene is of a group of people around a table, Bree and Britt, Joey and his mom and dad, and Dustin. They are all waiting for Dominique but she is forty minutes late. Joey's mom talks about doing a duet with Dominique and how it would help Joey. Joey claims that Dominique is not cool and Dustin talks about how Dominique dissed Joey and called him overrated on TRL. Finally Dominique enters in an extravagant dress and is just being Dominique. Bree and Britt continue to be creepy and hit on Joey. As the luncheon goes on, Joey finally gets tired of everyone and decides to leave. He claims he will not do a duet with Dominique and how they are all nuts, including his parents, He stands up and at the exact moment runs into Mary who is carrying shrimp. The shrimp flies all over the table and Mary and Joey share another moment. He lands on her but he stands up and helps her up. Then he leaves. Dominique then revokes Mary's phone privileges for a month and makes her clean the room within thirty minutes and leaves after Joey.
The next scene is Mary and Tami in Mary's bedroom and Mary claims she doesn't want to go to the ball but Tami persuades her too. Bree and Britt overhear this and complain to their mom who then makes Mary clean her bedroom. Dominique is going partying and she wants her room clean by midnight when she returns. Mary tells Tami she can't go and starts cleaning the room. The room is disgusting. Mary finds their lost dog Manson who's been gone since Christmas in Dominique's pile of clothes and sets him free as the doorbell rings with Tami at the door with their dresses. Tami has brought help in the form of a cleaning company owned by her sister's boyfriend's cousins. Tami and Mary enter the ball looking absolutely stunning. Bree, Britt, and Natalia try to look for Joey. note this is a black and white ball includes masks so no one knows who anyone is. Mary and Joey are talking at the punch bowl. Joey then asks Mary to dance and she gives her zune to the DJ. A tango starts playing and they start dancing. Mary shows off her dance skills and Joey is surprised. They share a dance together when everyone starts dancing. Bree and Britt then drop a bowl of m&m's to make Mary fall. Joey then rips of his mask but the clock starts to ring fifteen minutes to twelve and Mary runs out of the ball but not before dropping her zune. Joey grabs it. Mary and Tami are talking about how Mary and Joey shared a dance but Mary is sad about falling. The van suddenly breaks down and Mary has to quickly run to the house and hide the cleaners. A drunk Dominique walks into the room surprised by the cleanness but breaks down to Mary about how she is not so popular and passes out.
The next morning at school people are still buzzing about the mystery girl with Joey while Mary listens. Then as the announcements come on Joey is then on the announcements. He claims last night was one of the best nights of his life and that he needs to find the mystery girl. He then states that if you are the mystery girl tell me the top four most played songs on the zune. Mary is in shock. At lunch girls are waiting in line but none of them are the one obviously and Joey starts to get discouraged. Mary and Tami are on the stairs watching and Tami tries to convince Mary to tell Joey its her. Mary then states about how Joey will not like her anyway so whats the point. Bree and Britt hear this and later blackmail her by stating they'll show the video on youtube if she tries to tell Joey its her. Bree and Britt later sneak into Mary's room to find the songs and go to school the next day to tell Joey but Joey knows its not them. As he walks out to the car Tami finally convinces Mary to tell Joey regardless of the video and so Mary tries. But joey blows her off as he thinks its a ploy from Dominique to get him to sing with her. Mary is hurt and walks back to Tami's van. Bree and Britt see this and try to connect to the youtube via phone (clearly not smart at all).
Next scene shows Bree and Britt's birthday party (they turn sixteen every year until Dominique tells them to stop (age insecurities). Dominique is singing her song at the party and no one is listening. Mary is serving food when Tami walks in. She is there to help. Dustin then walks into the party to scope out the scene for Joey as he waits in his car. Dustin says that he'll find the mystery girl when he runs into Tami. He instantly recognizes her as his mystery girl from the dance. They share another flirtation when Dustin brings up Tami's friend and Tami states she's there. Dustin then reveals about how Joey is going crazy over her and Tami freaks out to find Mary. Dustin then calls Joey to tell him he found her to and come in. Joey walks in and Dominique finds him. She tries to convince him to do the duet but he blows her off again. He finds Dustin and Tami pushes Mary over the Joey. She tries again to tell him but is interrupted by a video playing on the big screen. It's the video of her when she was eleven revealing her crush on Joey. She runs away crying while everyone is laughing and Joey is trying to tell her its okay. She runs into her room and rips off her maid coat. She then runs out with her radio and plays it loudly by the pool. Its the song they were dancing to at the ball. Joey hears it and looks out the window to see Mary standing out in the cold. He walks out in awe realizing Mary is the one. Mary is still skeptical and tells Joey she doesn't need his charity. He claims that he really does like her and asks if he can take her out. Dominique then yells at Mary through the speakers that she needs her. Mary walks away after saying Yes.
The next morning Mary wakes up and goes straight to the mailbox. She runs out screaming and is riding through the halls of the school on her skateboard when she runs into Joey. She is explaining about how she got a letter saying she was in the top twenty out of five hundred applicants to a scholarship to the Manhattan Academy of Performing Arts and that they're going to call her for an audition. Joey hugs her and asks if she needs any help with dance moves. She tells him to meet her tomorrow. The next scene is of the phone call. Manhattan calls the house but Dominique answers. In the end Dominique tells them that Mary has two broken legs and cannot dance. She then leaves for las vegas as Mary and Joey pull up to the house. Someone has left Mary a long list of chores but her and Joey dance through the chores. Bree and Britt and Natalia are watching and angry at the result. They were hoping the chores would make Joey leave. Joey and Mary are chilling in her bedroom. Joey is strumming a guitar and Mary is laying on her bed. Joey then sings Mary a song he is writing and asks her to sing too. At the end they lock a moment and Mary playfully pushes Joey off the bed where he then sits back down in the chair. Joey talks about how he forgot why he started dancing. That is until he met her. They share another moment and they plan to meet again tomorrow.
Mary is in the kitchen when the sisters walk in and talk to Mary asking her if he left because he realized how lame she was. Then the doorbell rings and the sisters make her answer the door. It's flowers from Joey asking her to meet him on his patio at midnight. As Mary walk towards the patio she sees Natalia and Joey in his bedroom. Mary assumes the worst and runs away dropping the flower and the gate clangs. Joey hears it and walks out. Turns out he's trying to make Natalia leave. It was a set up.
Mary walks home but it takes allnight and she has been crying. Dominique is sleeping on the couch when she hears her and wakes up. She tells Mary to not cry about Joey because he is a E true story waiting to happen. And also tells Mary she was rejected from Manhattan.
Next day at school, Joey and Dustin are talking to a crowd of people. Then Joey sees Mary and chases after her. He asks if he's done something wrong when Mary gives him a cold look. Mary claims that they're done and Joey asks why. Then Mary asks if joey felt sorry for her and thats why he took her out. She also stated that she fell for him because she hoped he was different. as he tries to convince her that he is, Mary states that she is done dancing and states goodbye and walks away. Joey and Dustin try to figure out what happened and find Tami. Tami blows them off but they find their way to talk to her. Tami tells them that Mary knows he cheated when Joey realizes what happened. They explain to Tami about how Natalia broke into his house and he was trying to make her leave. Tami then agrees to help him. Joey wants Mary to come to his competition.
Next scene is Tami and Dustin pulling up to Mary's house when she is taking the trash out. They coax her into wearing something nice and going with them. They take her to the competition and at first she is upset but she relaxes. The competition begins. Dominique comes as well but there is someone else who comes who is later revealed as the audition correspondent for Manhattan (part of Joey's plan). As the dancers dance, even Bree and Britt who dance horribly and is booed off the stage, the competition ends with Natalia but not before Joey and Mary make eye contact but she breaks it. Dustin claim its not over yet and Joey Parker comes out to perform. He stops his performance to state he needs someone special with him. He calls out Mary's name to dance with him but looks to where she was standing to see she is gone. They start calling out her name. Finally someone sees her and Joey finds her. He akss mary to dance with him but she declines. This starts the playful banter they share as Joey tries to coax her on stage but Mary is adamant. Finally Mary goes on stage and they have a dance battle. Clearly Mary is still mad at Joey. But they finally start partner dancing and it shows Mary's true talents. The songs plays out and Joey starts singing and asks for Mary's help so she starts singing too. The performance plays out well by the crowd. When the song ends Mary looks at Natalia and rushes off stage. Joey tells the crowd that they will announce a winner in five minutes and runs after Mary clearing up any doubts about their relationship stating there is nothing between him and natalia. Mary is finally convinced and Joey gets the results. Surprise surprise Mary is the winner and Bree, Britt, Natalia, and Dominique are furious. Natalia at least admits that Mary is good and runs away crying. Dominique walks up to them and is angry at Mary claiming she's embarrassed that her maid won the JP competition. The audition correspondent also walks up to them congratulating Mary and stating that she won the full scholarship and states she'll call her Monday with the details. Dominique walks away but falls off the stage and Mary and Joey share a kiss. (finally).
The next scene is of Mary putting her trunks into the van with the help of Dustin, Tami, and Joey and she states how her dreams are all finally coming true. Dominique (ironically broke both legs) rolls up to her in a wheel chair in a final attempt to prevent Mary from leaving stating she needs her help. Tami, Dustin and Mary share a final goodbye. Joey and Mary drive away in the moving van but not before sharing another kiss.