Five high school kids, Olivia, Wendall, Stella, Charlie, and Mo, meet in detention and start a band based on the lemonade vending machine outside the detention room. ## Personality High school freshmen Olivia White, Mohini "Mo" Banjari, Charles "Charlie" Delgado, Stella Yamada, and Wendell "Wen" Gifford meet while in detention. When Miss Reznick, the music teacher supervising detention, leaves briefly, they tap out a beat and play instruments, with Olivia singing along. Miss Reznick returns and encourages them to enter the upcoming Rising Star music competition, in which the popular band Mudslide Crush is also slated to perform in. The band forms with Olivia on lead vocals, Stella on lead guitar and backing vocals, Mo on bass and backing vocals, Wen on keyboards, keytar, and rapping vocals, and Charlie on drums. At school, Stella spits lemonade on Ray Beech, lead singer of Mudslide Crush, when he ridicules Olivia for her stage fright. He refers to her as "Lemonade Mouth", giving the band its name. The band later discovers the school's lemonade machine is being removed, to their horror. Stella enters the band in Rising Star as well as the upcoming Halloween Bash, much to Olivia's chagrin, and begins to feel anxious. Mo breaks up with her boyfriend Scott Picket, Mudslide Crush's guitarist after she catches him flirting with a cheerleader. Before performing at the Halloween Bash, Olivia disappears. The band eventually finds her in the bathroom, where she is feeling nauseous and suffering a panic attack. They tell her that they all believe in her. This encourages her to perform, after which Stella speaks to the crowd, objecting to the removal of the lemonade machine and encouraging her fellow students to freely express themselves. The principal, Stan Branigan, angrily bans them from playing at school again. The next day, banners in support of Lemonade Mouth were posted around the school, raising their spirits. When Olivia is absent from school one day, the band gets worried. They later visit her and learn that her cat Nancy, her only remaining memory of her late mother, has died, which has left her in a depressed state. They begin to grow closer to one another, opening up about each of their struggles. They also learn that their song "Determinate" is being played on the local radio. Shortly after, however, things begin to go downhill for the group; Mo contracts the flu, Charlie breaks his fingers, Wen injures his eye, and Olivia loses her voice during an argument with Wen. The members of Lemonade Mouth joined the school to protest the removal of the lemonade machine. After being detained by police and contemplating the future of the band, they agree to perform at Rising Star. As each of their parents and guardians come to retrieve them from the police station, they reconcile their individual problems at home; Wen finally accepts his dad's girlfriend, Olivia gains the courage to send a letter to her incarcerated father, Mo gets her dad to accept her for who she is, Charlie realizes he doesn't have to live up to his older brother's prowess, and Stella realizes she doesn't have to be a genius to fit in with her family. While performing at Rising Star, Olivia and Mo's respective injuries begin to resurface in the middle of their performance. Dejected, the band is about to exit the stage when the audience begins to sing their song to support them. Scott fed up with Ray's hostile treatment towards Lemonade Mouth, leaves Mudslide Crush and plays his guitar alongside the audience, bringing Lemonade Mouth back onto the stage to successfully finish their performance. Sometime later, things get better for the band: Mo and Scott have gotten back together, Charlie (who had developed a crush on Mo while forming the band) takes an interest in a new girl, Wen accepts Sydney, Stella meets Mel, the original owner of the organic lemonade machine, who helps donates a new music auditorium to the band's school with Principal Branigan's approval, and Olivia regains her voice. Wen also gives her a new kitten and apologizes to her about their fight. This gesture touches Olivia and the two reconcile. Later, Olivia mails the entire story to her father. The film closes with Lemonade Mouth performing at Madison Square Garden, with Scott as their new rhythm guitarist.

Olivia: Oh, no, no, Wen, this isn't about Lemonade Mouth. This is about you not appreciating what you have. You have a family! Your dad, your sister, Sydney! I don't even remember my mom; I haven't talked to my dad in years - and you have the nerve to feel sorry for yourself? Wha... Okay! No! Fine! Go ahead. Give up! See if I care! I didn't even know what to be in this band in the first place. Wen: Then why did you DO it? Olivia: [shouting at first and then quietly] FOR YOU, YOU JERK! I did it for you. Stella: What happened? Did you all get hit by a bus or something?