After Caleb is released from custody, he must make some decisions about the Newport Group, and his decisions don't sit well with Kirsten. Seth is determined to win back Summer's friendship, even if it means getting a job. Ryan has a string of awkward encounters with a new girl at school, while Marissa faces being alone.

It's a new era in Newport Beach. Kirsten and Julie try and work together at The Newport Group, while Sandy tries to find out what Caleb is hiding. Seth and Ryan go on a double date with Lindsay and Alex, but it ends differently than the four of them might have expected.

It's the annual "SnO.C." winter dance. Seth wants to take his relationship with Alex further, but she might have other plans. Marissa's secret relationship with D.J. is exposed, while Zach continues his pursuit of a Seth-free relationship with Summer. Sandy solves Caleb's legal puzzle ending with a shocking twist.

It's Chrismukkah once again in The O.C. and this year, Seth wants to take it global. As Caleb is faced with the looming prospect of going to prison, Sandy convinces him to come forward and reveal the truth about his involvement with Renee. Julie and Jimmy spend some quality time together. Caleb's confession shocks the Cohen and Nichol family to the core, and nothing will be the same again.

After Caleb's confession, The Cohens try to welcome Lindsay as part of the family. Jimmy is faced with a choice when Marissa finds out about his relationship with his ex-wife, Julie. Seth attempts to be a "bad boy" like Ryan to impress Alex. Summer finds out what Zach did on his Christmas break while Ryan and Lindsay want to know if it is too awkward for them to be together.

When Sandy forgets his and Kirsten's 20th wedding anniversary, he finds himself going to a lot of trouble to make it up to her. Seth and Ryan's respective relationships with Alex and Lindsay add to the trouble, and doubt falls upon their futures together. Marissa and Julie continue to butt heads over DJ, and Summer wants to take her relationship with Zach to the next level.

Seth is thrown when Alex's ex arrives in town for a visit, and is even more thrown when he finds out who it is. Julie has a plan to try and save The Newport Group, which to everyone's surprise, might actually work. Lindsay sticks out when she joins Summer and Marissa for a girls night out; meanwhile, Ryan, Seth and Zach contemplate playing it safe on a guys' night in. But nothing ever goes as planned.

Things heat up between Sandy and Kirsten when Sandy decides to help his mentor in law school find his daughter, Rebecca, whom was Sandy's first love. Seth and Zach start up a comic book based on their lives in Newport, while Summer questions why she's been left out. Ryan makes the attempt to unite Lindsay and Caleb after Lindsay tells Ryan she is curious in getting to know her "new" father. While Julie is in Paris, Marissa looks for new ways to rebel; in doing so, her friendship with Alex increases.

After hearing about Lindsay and Ryan's failed attempt at dinner with Caleb the night before, Kirsten arranges a dinner that she can supervise. But her presence makes no difference when Ryan and Caleb butt heads and disaster strikes. Sandy keeps Rebecca's presence in Newport a secret from Kirsten after deciding to take her case to court. Marissa and Alex's relationship intensifies, while Seth and Summer spend a lot of time together at Zach's insistence.

It's Valentines Day 2005 in O.C. when Sandy and Kirsten's conflict about Rebecca continues. Ryan tries to make peace with Caleb to spend Valentines Day with Lindsay. While Seth, Zach, and Summer head to San Diego in hope to make their Comic Book idea succeed Seth has a breakdown and ends up in a lonely state. Marissa and Alex take a step forward in their relationship while Julie returns from her trip in hope to reconnect with Marissa.

As Sandy continues working on Rebecca's case, Kirsten questions how strong their feelings are for one another. Seth continues his downward spiral in the aftermath of Zach and Summer's Valentine's night together, while Marissa confronts her fear about her relationship with Alex. Caleb offers Lindsay a place in his family, but not without a paternity test.

It's a rainy day in Newport where Lindsay decides to take the DNA test and makes a difficult choice regarding her life with Caleb while Ryan helps her through it. Sandy still wants to help Rebecca with her case and tries to convince her not to run again. Kirsten is still upset and wishes her marriage would go back to normal and for Rebecca's case to be over with. Meanwhile, Seth thinks he's lost Summer forever untill Summer is unable to hide from her feelings once and for all. Marissa moves out of the Cooper-Nichol mansion and moves in with Alex after she tells her mother about Alex being her girlfriend.