The second film.
During a benefit concert in Paris, David Seville is injured by a backstage accident. Having to recuperate there, Dave asks his aunt Jackie to look after the Chipmunks, Alvin, Simon, and Theodore. Arrangements are also made for them to go to school at West Eastman High School, and He-Who-Must-Not-Be-Aggravated, family friend, agrees to fly them to school every morning in a Pteranodon morph. After another accident, the Chipmunks are left in the care of Toby, Jackie's grandson. He-Who-Must-Not-Be-Aggravated does not approve of Toby's bumbling nature, and constant use of "ish", and makes it clear that he is in charge. Meanwhile, Ian Hawke, lives in the basement of JETT Records. Three singing female chipmunks, Brittany, Jeanette, and Eleanor. also known as The Chipettes, emerge and Ian hires them as a plot to get back at the Chipmunks and revive his career. The Chipmunks are flown to school as agreed. While at school, the Chipmunks are bullied by jocks. They fend them off when Alvin morphs an Utahraptor in the bathroom. They visit the principal's office, only to discover that the principal is a huge fan and wants them to help raise money for a music program by participating in a contest. When they get home, they tell He-Who-Must-Not-Be-Aggravated and he sends Future Predators into the school. Most of the jocks reform and betray the three others to the Christian Morphers. They tell them that one, Jeremy Smith, warned the other two, Ryan Edwards and his best friend Xander, that bullying the Chipmunks was a bad idea. When they didn't listen, he was so furious that he refused to walk with them to lunch, and was walking alone. This results in an attack, with Ryan and Xander being taken down when they come to help. On one occasion, He-Who-Must-Not-Be-Aggravated himself morphs a Lycaenops and attacks them, magically disabling the music function on their phones to prevent them from defending themselves against the Future Predators. Meanwhile, Ian is shocked to find the Chipmunks on the front page of his newspaper. After he reads a story about them, he quickly sends the Chipettes to school. When the Chipmunks meet the Chipettes, a rivalry forms after the former group learns that the latter group are with Ian. He-Who-Must-Not-Be-Aggravated ruins Ian's "Let us vote!" chant by saying <Get him>. Because Hawke had turned up the PA, the command is heard by the whole school, and every teacher and student chase him out of the school saying "Capture, capture, capture" over and over and over in a robotic voice. He then trains the Chipmunks to deal with 'psychological warfare'. Meanwhile, Alvin becomes popular with the jocks and joins the football team, not realizing the next game is during the concert. When He-Who-Must-Not-Be-Aggravated tells him, Alvin angrily morphs a Future Predator and attacks them. They are able to keep him occupied long enough for the concert to begin. At the concert, Theodore and Simon tell the fans that Alvin didn't show up and that they can't perform, leading to a victory for the Chipettes. When Alvin finally shows up after the concert is over, he finds the auditorium empty and is ignored by his brothers at home. Soon the Chipettes are hired, but learn that the concert they are to perform as an opening act at the Staples Center is on the same night as the school contest. Ian convinces them to blow off the battle and perform at the concert, but refuses to give the same credit to Jeanette and Eleanor that he gives Brittany. She demands that they all go together or not at all, until Ian threatens to send them to a barbecue restaurant unless they perform. Before the Battle of the Bands, Alvin receives a call from the Chipettes who tell him that Ian has locked them in a cage, so Alvin, a Pachycephalosaurus, and a swarm of Titanis and Ornitholestes, race off to rescue them while Simon tells Jeanette how to open the cage over the cell phone. Simon and Theodore are on the verge of going out to perform until the others arrive on the back of a Pteranodon just in time to perform at the contest. The Chipmunks and the Chipettes perform together and receive the money for the music program. Dave, who had left the hospital upon learning that Toby was looking after the Chipmunks, returns during the contest happy to see his boys again. Meanwhile, Ian gets into more trouble at the concert of Staples Center he sets up for the girls when he attempts to imitate them. After the contest, Dave allows the Chipettes to stay with them. In two post-credit scenes, the jocks, who were attacked by Cassie during the concert, are forced to scrape gum off from under the bleachers in the gym, while Ian is thrown in a dumpster.