It's Ashley's birthday and she's having a party at her house. During the party Chloe meets Zack. She is a wealthy girl living in Malibu, while he is a lower class guy living in the valley. Chloe's brother gets into a fight with one of Zack's friends, Flipper. This leads to the arrest of both. Ashley and her upscale friends, Julie and Bree, dare Nina. They want her to try and sleep with her best friend, Chloe's, brother. She does the deed, breaking a previous promise that she made to Chloe. Due to the fight at the party, Zack's parents think that he should live with his sister in Malibu. Meanwhile, Josh gets pulled from the school's football team. Chloe's friend Teddy becomes an arsonist when he sets his own home on fire to try and blame it on Zack. Even worse, an earthquake destroys the high school in the valley, making it so that the two rival schools must combine, and all of the valley kids must now attend school in Malibu.

It's Ashley's birthday and she's having a party at her house. During the party Chloe meets Zack. She is a wealthy girl living in Malibu, while he is a lower class guy living in the valley. Chloe's brother gets into a fight with one of Zack's friends, Flipper. This leads to the arrest of both. Ashley and her upscale friends, Julie and Bree, dare Nina. They want her to try and sleep with her best friend, Chloe's, brother. She does the deed, breaking a previous promise that she made to Chloe. Due to the fight at the party, Zack's parents think that he should live with his sister in Malibu. Meanwhile, Josh gets pulled from the school's football team. Chloe's friend Teddy becomes an arsonist when he sets his own home on fire to try and blame it on Zack. Even worse, an earthquake destroys the high school in the valley, making it so that the two rival schools must combine, and all of the valley kids must now attend school in Malibu.

Everyone needs some time to adjust as the two high schools are mixed together. Teddy finds it hard to go back to school only to be known as the kid that torched his own house. Zack is asked to join a special advanced English class, which his friends can't understand. Kacey is continually harassed by the popular clique at school, most of the comments referring to her weight. This makes her decide that leaving school would be the best option. And Flipper's brother Sandy pays him a visit after being released from jail. Zack opts to spend time with an upset Kacey instead of showing up to Chloe's for dinner (without even calling), which leaves Suki with a bad impression of him. Later, Josh decides to throw a party while his mom is out of town.

Chloe is sexually harassed by her art teacher when he asks her to paint a mural, but is clearly interested in more than her artwork. Meanwhile, Marc and Suki decide to give dating a try. And Josh and Nina discuss their own relationship.

Jack Walker, Josh and Chloe's father decides to pay the family a visit. Both Josh and Chloe feel the tension in their home and decide to break the rules. Josh goes on a drinking binge while Chloe decides to lose her virgin status. Meanwhile, Nina has a pregnancy scare, Zack's guy friends hide a video camera in the girl's locker room at school, and Kacey decides to once again attend school.

Zack has trouble keeping up in his new English class. Meanwhile, Nina and Josh are tempted to be with other people while Nina's out of town. Kacey keeps a huge secret to herself- she and her mother are now out on the streets. Her mother takes a job as a maid and move into the Walker's apartment over the garage.

Zack and Chloe battle in the election for class president. Ashley decides whether or not she should quit the track team. She wants more time to spend with friends, but her mother will only be happy if she's on the team. Meanwhile, Nina and Josh break up and Josh immediately finds comfort in the arms of an older woman named Jill. Things heat up between Bree and Teddy as well as Kacey and Seth, until Seth tells everyone that he got more action than he really did.

Mouse accidentally becomes an accessory in a robbery when he hangs out with his brother's gang members. Meanwhile, Josh and Nina try to find Teddy a date as everyone else tries to set themselves up for the Edwin McCain concert. Flipper scores backstage passes, but Ashley won't believe it.

Zack volunteers to work at a teen hotline, and he's surprised to hear a familiar voice on the line- Chloe's. She tells him about her problem with bulimia. Nina ends up in a bad situation when she finally gets the upperclassman that she's had her eye on. Meanwhile, Flipper tries to get closer to Ashley by giving her tips on how to get Josh.

In the series finale, Zack takes the fall a beer can in Josh's car, after Suki spies it. She decides that Zack is completely unfit for Chloe. The upperclassman that Nina had her eye on takes his own fall as he tumbles down some bleachers, making Zack and Teddy look guilty of attempted murder, if not murder. While supposedly dealing with her bulimia, Chloe escapes from the hospital. She and Zack runaway together, driving off into the sunset.