The O.C.

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. Meanwhile, Sandy and Kirsten take advantage of an opportunity to bond with Ryan, who is in a Taylor-induced haze. Kaitlin meets the mean girl of Harbor School and tries to best her by throwing a huge party at the Roberts house. Julie learns that Newmatch is more than just a dating service. And the truth about Che (recurring guest star

It's time for another Chrismukkah in Orange County. After Ryan and Taylor have an accident while hanging holiday lights, they realize that everything is not as it seems, and they must do whatever it takes to make things right again. Former series star TATE DONOVAN guest stars as Jimmy Cooper.

As the new year approaches, Ryan plans a special surprise road trip for Taylor and himself.

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.

Taylor's ex-husband, Henri-Michel (HENRI LUBATTI), gets a little too close to home while promoting his erotic memoirs. After Henri-Michel tells Ryan about Taylor's exciting life in France, Ryan questions his own relationship with Taylor. Meanwhile, Seth visits Dr. Roberts (recurring guest star MICHAEL NOURI) in Seattle to ask for permission to marry Summer, who gets a vision of her future. And Kai

Che (recurring guest star CHRIS PRATT) and Seth take a trip to a forest, where Che has a dream and discovers that his spirit might be in love with someone unexpected.

As the Cohens prepare for Kirsten's 40th birthday party, Kirsten gets some news that will change her life forever.

As Valentine's Day approaches, Ryan worries that the pressure of the holiday will ruin his relationship with Taylor.

Taylor eagerly prepares for her first real birthday celebration, but she frets over the fact that Ryan has still not told her he loves her.

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.

In the emotional series finale of "The O.C.," Ryan, the Cohens, the Coopers and their friends build new lives, resolve lingering issues, face major decisions and undergo shocking personal transformations. No matter what happens or where they go, the members of this unique extended family all know that they will always have one another to turn to.