Act One

On the front steps of East High, it's the first day after winter break. Troy, the captain of the basketball team, greets his teammates. Gabriella, the shy, smart, new girl meets the rest of the braniacs, who welcome her to their fold ("Wildcat Cheer"). The Jocks, Brainiacs, Thespians and Skater Dudes find their cliques. Troy and Gabriella each describe their winter adventures to their respective friend groups, not realizing that the other is nearby. They met at a ski lodge and ended up performing a karaoke number together. It was like a romantic dream. Their excitement leads the other kids to start talking about their own New Year's resolutions ("Start of Something New").

In Ms. Darbus' homeroom, Troy spots Gabriella and realizes that she has just transferred to East High. When he calls her to get her attention, the eccentric drama teacher quickly confiscates all cell phones and assigns detention. Gabriella and Troy can't believe that they have ended up in the same school.

Between classes, Gabriella and Troy look at the audition sign-up for the school musical. They are nervous about signing up, but remember the good time they had a karaoke. The drama diva, Sharpay, drops by and discourages Gabriella from auditioning. She is interested in both the lead part... and Troy... for herself. The incident with Sharpay and Gabriella has made Troy late for basketball practice. He is also distracted by thoughts of Gabriella and the musical. The coach, Troy's father, is not pleased; neither are Troy's best friend Chad and the rest of his teammates. They tell Troy that he has to focus on the upcoming championship game ("Get'cha Head in the Game").

In math class, Sharpay tries to dampen Gabriella's interest in Troy. Meanwhile, Gabriella gets a question right that the teacher had wrong. Taylor, the science club president, encourages Gabriella to join the science decathlon team. There is a big meet coming up, and Taylor knows that they can with Gabriella's help. Gabriella is uncertain for the same reason that she was uncertain about auditioning: she wants to get acclimated to her new school before joining activities. Sharpay, however, has other plans – she plants information in Taylor's locker that proves Gabriella is a genius.

In detention, Ms. Darbus gives the students an acting lesson. Coach Bolton interrupts; he is furious with her for keeping his team from practice. They face-off in a classic debate – arts versus sports.

The next day, hopeful Thespians strut their stuff for Ms. Darbus ("Auditions"). The other auditioners are no match for Sharpay and twin brother, Ryan, but despite their obvious talent, this team lacks soul ("What I've Been Looking For"). Troy and Gabriella arrive too late to audition, but Kelsi, the show's composer, plays the song the way she had intended for it to be sung, as opposed to the version Ryan and Sharpay performed. She encourages Troy and Gabriella to sing it the right way, and they do ("What I've Been Looking For – Reprise"). Ms. Darbus overhears and gives them a callback. News of Troy and Gabriella's audition spreads fast ("Cellular Fusion"). Sharpay is furious... and she's not the only one.

In the lunchroom, the Jocks and Braniacs try to explain to Troy and Gabriella, respectively, why they should not venture outside of what they know and what they are good at. They disagree, encouraging other students in other cliques to reveal their secret – and sometimes contradictory – interests. ("Stick to the Status Quo"). Zeke's interest is baking, and he tries to impress Sharpay with a cake... but it ends up falling on her head.

Act Two

Troy and Gabriella escape to the rooftop garden and share a little bit about their real selves; they are quickly falling for each other ("I Can't Take My Eyes Off of You"). Gabriella wishes that high school could be more like kindergarten – that people could be friends based on who they are, not on what they can do. Zeke tries to apologize to Sharpay; he offers to bake her something else, but she'll have none of it. Meanwhile, the Jocks and Brainiacs devise a plan to trick Troy and Gabriella into forgetting about the musical and committing to their respective competitions. Sharpay plans to lie to Ms. Darbus and say that Troy is only auditioning to sabotage the musical. The cheerleaders practice in the gym ("Wildcat Cheer – Reprise").

Gabriella sees Troy practicing basketball drills. Coach Bolton interrupts them and has Gabriella leave. He tells Troy that his team is counting on him and discourages him from distractions like Gabriella and the play. Troy is not pleased with this sentiment.

The lights come up on Troy and Gabriella, each coming in late to practice. Citing examples of famous athletes and braniacs, their respective teammates tell them they need to focus on what's important: basketball and science decathlon, not singing ("Counting on You"). Then, the Jocks and Braniacs enact their plan, which involves a secret phone call that makes it seem as if Troy is dismissing Gabriella and the callback. She dismisses him in return. Both Troy and Gabriella are crushed. Their teammates immediately regret having caused them so much pain ("When There Was Me and You").

Later, Ryan tells Sharpay that she needs to calm down and stop sabotaging Troy and Gabriella; it's not the end of the world if they don't get the leads. Sharpay disagrees. She believes that she is defined by her success as an actress and doesn't know who she is without it. Meanwhile, Gabriella and Troy make up and practice with Kelsi to get ready for the callback ("Something New – Reprise"). However, believing Sharpay's lie that Troy is trying to sabotage the audition, Ms. Darbus decides that he will need to prove he really wants it. She schedules the callback at the same time as the championship game and the decathlon. Chad and Taylor come up with a plan that will allow Troy and Gabriella to do both the competitions and the callback ("We're All in This Together").

While the Jocks and Brainiacs compete, Sharpay and Ryan pull off a polished callback performance ("Bop to the Top"). When Taylor's laptop shuts down the electricity, Troy and Gabriella rush to the theatre... but they arrive too late. Still, when the East High students from all of the different cliques show up to rally behind them, Ms. Darbus is moved and pleased by the attention the theatre department is getting. Ryan tells her that Sharpay lied about Troy trying to sabotage auditions. Kelsi stands up to Sharpay, as well, and demands to play for their audition. They deliver on the callback, and Ms. Darbus gives them the lead roles ("Breaking Free").

Back at the gym, the Wildcats win the game and the Braniacs win the science decathlon. Coach Bolton is impressed by Troy's singing and encourages him to do whatever he wants. He and Ms. Darbus make up; Sharpay and Gabriella also reconcile when Sharpay realizes that Zeke likes her for her, not because she's a star. The whole school comes together as winners, and Troy points out to Gabriella that it is just like kindergarten – everyone is getting along based on who they are, not because of what they do ("We're All in This Together – Reprise").