Everyone struggles to adjust to life without Marissa. Ryan has moved out of the Cohen house. When Ryan misses a special dinner, Seth finds him in the wrong part of town and calls Summer for help. Meanwhile, Julie Cooper will do anything to avoid dealing with the loss of Marissa. Taylor Townsend hides out in the diner and tries to convince her friends she is in Paris.

Ryan travels to Mexico--with Seth in tow--to put an end to his turmoil in the only way he knows how. Meanwhile, Seth meets some new friends there who help him find what he is looking for. Harbor School's new female dean of discipline forces Kaitlin and Julie to work together on Harbor's clothing drive. The Cohens ostracize Julie when they discover that she was part of Ryan and Seth's activities.

It's Thanksgiving morning at the Cohen house, and the family is still dealing with what happened in Mexico. Sandy makes a deal to help Volchok but lets Ryan settle the score. As Summer packs for a trip home to visit her family and Seth for the holiday, she wonders if she can deal with Newport anymore. And unable to cope with either Kaitlin or Dr. Roberts, Julie spends most of Thanksgiving alone.

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 take their activism to a new level, resulting in more freedom than they expected. Meanwhile, after Julie flirts with a tennis instructor whom Kaitlin likes, the younger Cooper gets her revenge at a charity party. Attracted to Ryan, Taylor tries to cure his insomnia with her own therapeutic plan. When her schemes fail, she turns to Kaitlin for advice on how to get her way with Ryan.

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 comes out.

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. But when Summer confronts Seth about not making any plans, Ryan's romantic getaway for two is spoiled. Later, Summer's future rests in the hands of a shady character that the gang meets on the way to Las Vegas. Meanwhile, Julie's accounting practices come under some unwanted scrutiny.

Newly engaged Seth and Summer both panic about the prospect of being married, but neither will break it off. Instead, they begin a complicated game of one-upmanship that almost leads them to Las Vegas for a wedding. Meanwhile, when Ryan's estranged biological father, Frank, who has been in prison for years, tries to reconcile with Ryan, Sandy remains dubious.

Taylor's ex-husband, Henri-Michel, gets a little too close to home while promoting his erotic memoirs. After he tells Ryan about Taylor's exciting life in France, Ryan questions his own relationship with Taylor. Meanwhile, Seth visits Dr. Roberts in Seattle to ask for permission to marry Summer. And Kaitlin realizes that she likes Will, but she is concerned he thinks she's too shallow.

Che 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. Seth and Summer finally speak for the first time since she rejected his marriage proposal. Meanwhile, Taylor decides that she can no longer associate with Ryan. Julie works her way back into Kirsten's life in the only way she knows how. And Kaitlin shuts out Will.

As the Cohens prepare for Kirsten's 40th birthday party, Kirsten gets some news that will change her life forever. Meanwhile, Julie is having a secret love affair. While Ryan acts as if he doesn't miss Taylor, a therapist gives her some rules to live by. Seth and Che's plan to save Newport's groundhog goes awry. And Sandy and Kirsten have surprises in store for each other.

As Valentine's Day approaches, Ryan worries that the pressure of the holiday will ruin his relationship with Taylor. Meanwhile, revelations from their pasts cause Summer and Seth to question whether they are destined to be together. Kirsten reminisces about her own history and decides to share a secret with Sandy. Ryan begins to tentatively reconcile with his father, Frank.

Taylor eagerly prepares for her first real birthday celebration but frets that Ryan has not told her he loves her. She has secretly applied to and been accepted at Berkeley, the same school Ryan is going to attend. Meanwhile, Kaitlin misbehaves in reaction to Julie dating Frank. Kirsten deals with catty Newport women in a yoga class. Summer wishes Seth were passionately interested in something.

In the aftermath of a major earthquake that cuts off power and communication, Ryan is injured and the boys are stranded on a deserted road. Summer and Taylor worry about their missing boyfriends while searching for Summer's escaped pet rabbit. Trapped in an ice cream shop, Julie and Kaitlin bond and deal with an amorous clerk--until they are saved by the only man in Newport for Julie.

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.