In the fourth season premiere, everyone struggles to adjust to life without Marissa.

Ryan travels to Mexico--with a stubborn Seth in tow--to put an end to his turmoil in the only way he knows how, but he comes up empty in quest for revenge. Meanwhile, Seth meets some new friends in Mexico, including a Marine (STEVE-O - "Jackass"), who help him find what he is looking for. Harbor School's new female dean of discipline, Dean Torres (TIA CARRERE - "True Lies," "Relic Hunter"), forces

It's Thanksgiving morning at the Cohen house, and the family is still dealing with what happened in Mexico.

When Summer tries to become the gossip-loving girl she once was, she realizes that Brown may have changed her forever. Fortunately, Seth continues to be supportive of the new Summer through all of her endeavors. Similarly, Ryan empathizes with Taylor and surprisingly helps her out of a bind. Meanwhile, Julie and Kaitlin attempt to stay out of trouble, but neither can resist temptation.

Summer and Che (recurring guest star CHRIS PRATT) take their activism to a new level, resulting in more freedom than they expected. Meanwhile, after Julie flirts with a hot tennis instructor whom Kaitlin likes, the younger Cooper gets her revenge at a charity party. But later, Kaitlin helps save Julie and Kirsten's dating service. Attracted to Ryan, Taylor tries to cure his insomnia with her own t

When Seth visits Summer at Brown, he finds an empty dorm room. Sandy and Kirsten take advantage of an opportunity to bond with Ryan. Kaitlin meets the mean girl of Harbor School and tries to throw a huge party at the Roberts house.

It's time for another Chrismukkah in Orange County. After Ryan and Taylor have an accident while hanging holiday lights, they realise everything is not as it seems, and they must do whatever it takes to make things right again.

Ryan plans a surprise road trip for Taylor and himself. When Summer confronts Seth about not making plans, Ryan's romantic getaway is spoiled. Summer's future rests in the hands of a character that the gang meets on the way to Las Vegas.

Newly engaged Seth and Summer both panic about the prospect of being married, but neither will break it off, despite the advice of their friends. They begin a game of one-upmanship that almost leads them to Las Vegas for a wedding.

Henri-Michel gets too close to home while promoting his memoirs. After Henri-Michel tells Ryan about Taylor's life in France, Ryan questions his relationship. Seth visits Dr Roberts in Seattle to ask for permission to marry Summer.

Che and Seth take a trip to a forest, where Che has a dream and discovers his spirit might be in love with someone unexpected. Afterward, Seth and Summer finally speak for the first time since she rejected his marriage proposal.

As the Cohens prepare for Kirsten's birthday party, Kirsten gets news that will change her life. Julie is having a love affair and Kaitlin is doing everything to stop it. While Ryan acts as if he doesn't miss Taylor, she visits a therapist.

As Valentine's Day approaches, Ryan worries the pressure will ruin his relationship with Taylor. Revelations, along with a psychic's dire predictions, cause Summer and Seth to question whether or not they are destined to be together.

Taylor prepares for her birthday celebration but frets over the fact Ryan has still not told her that he loves her. Even more concerning is that she has applied to and been accepted at Berkeley. And an earthquake shakes Newport Beach.

In the aftermath of a major earthquake that cuts off power and communication between the Cohens and their loved ones, Seth must take over Ryan's role as the protector when Ryan is injured, and the boys are stranded on a deserted road.

The Coopers and their friends build new lives, resolve lingering issues, face major decisions and undergo shocking personal transformations. No matter what happens, the members of this family know they will always have one another.