Seth excitedly introduces a skeptical Ryan to Chrismukkah, a Cohen family tradition that resulted from Kirsten being Christian & Sandy being Jewish. As everyone prepares for a huge holiday party organized by Julie (recurring guest star MELINDA CLARKE), Seth continues attempting to juggle Anna (recurring guest star SAMAIRE ARMSTRONG) & Summer (recurring guest star RACHEL BILSON), both of whom want to date him exclusively. Meanwhile, on opposing sides of a lawsuit, Sandy & Kirsten dread working through the holiday season, but Kirsten learns something about her father that could change everything. & Ryan & Marissa's shopping trip leads to trouble--and the beginning of even bigger problems for Marissa. ...

Kirsten's rebellious 25-year-old sister, Hailey Nichol (recurring guest star AMANDA RIGHETTI), comes to town on New Year's Eve, causing turmoil in the Cohen household. Ryan & Marissa plan a quiet evening of popcorn & movies at home, but Marissa later decides to attend a party hosted by a young man, Oliver Trask (recurring guest star TAYLOR HANDLEY), who goes to the same therapist as she does. Meanwhile, Hailey persuades Sandy & Kirsten to go out so she can have a raging party in their house for a few friends. As the clock ticks closer to midnight, Ryan hopes that he can make it to Marissa in time for their first New Year's kiss together. As of this episode, MELINDA CLARKE as Julie Cooper & RACHEL BILSON as Summer Roberts are series stars. ...

Kirsten's unemployed sister, Hailey (recurring guest star AMANDA RIGHETTI), moves in with the Cohens & disrupts the entire family when she behaves as the houseguest from hell. Hailey depletes the refrigerator, controls the television, disrespects Kirsten & shows no signs of leaving anytime soon. Desiring some time alone with his wife, Sandy urges Kirsten to resolve the problem with her sister. When Kirsten can't confront Hailey, Sandy angrily tells Hailey that everyone is tired of tolerating her rude behavior. Meanwhile, Seth & Anna (recurring guest star SAMAIRE ARMSTRONG) struggle with telling Summer the truth that they are now a couple. Ryan feels jealous about Marissa's new friend, Oliver (recurring guest star TAYLOR HANDLEY), a neglected, drug-abusing teen she met in therapy who always seems to show up when Ryan wants some privacy with Marissa. Later, Ryan helps Oliver by asking Sandy to intervene when Oliver is arrested for trying to buy drugs from an undercover cop. ...

Ryan, Seth, Marissa, Anna (recurring guest star SAMAIRE ARMSTRONG), Luke & Summer head to Palm Springs for a parent-free weekend at the home of Marissa's new, troubled friend Oliver (recurring guest star TAYLOR HANDLEY). Hoping to spend some time alone with Marissa, Ryan, who is neither interested in golf nor spas, reluctantly agrees to make the road trip with Luke. Oliver quickly irritates Ryan by flirting with Marissa & deliberately keeping the couple apart. & Summer uses every method she can to annoy Seth & Anna. The weekend goes from bad to worse when Oliver angrily leaves the house only to later phone Marissa with news that he's taken a handful of drugs to commit suicide. Marissa & Ryan race to a hotel where Oliver seems to be shaken but in no apparent danger of overdosing. Ryan is unconvinced that Oliver even attempted to take his life, & much to Ryan's dismay, Marissa insists on staying the night alone with Oliver. ...

Sandy & Jimmy begin a new business partnership when they buy The Lighthouse, a beloved Newport restaurant. Meanwhile, Kirsten & Julie become workmates when Julie is hired as Newport Group's new model-home designer. Also, Seth's jealousy of Summer's new boyfriend causes Seth to doubt his relationship with Anna (recurring guest star SAMAIRE ARMSTRONG). & Ryan loses control while trying to prove that Marissa's troubled friend Oliver (recurring guest star TAYLOR HANDLEY) is a fraud, leaving Seth & the Cohens concerned & afraid for Ryan. ...

Marissa tries to mend her relationship with Ryan, but he can't forgive her for the situation with Oliver. Things become even more complicated when Theresa (recurring guest star NAVI RAWAT), Ryan's ex-girlfriend from Chino, arrives to waitress at Kirsten's Valentine's Day dance. Meanwhile, Seth & Summer decide to take their friendship to a new level, & Jimmy finds out he has a secret admirer. ...

Marissa & Ryan try to start over as friends, but it's not as easy as they had hoped. As Theresa (recurring guest star NAVI RAWAT), Ryan's ex-girlfriend from Chino, begins spending more time in Newport, Ryan discovers that she hasn't been honest about why she's there. Seth believes his relationship with Summer is great, but when she refuses to acknowledge him at school, he feels he has to teach her a lesson. Meanwhile, Sandy finds himself embroiled in another mess created by Caleb (recurring guest star ALAN DALE). & Jimmy begins to suspect something is going on between Julie & Luke. ...

When Theresa (recurring guest star NAVI RAWAT) decides to stay in Newport, Ryan is glad, but he feels obligated to help her find a job & a place to live. Julie & Luke's affair continues to flourish, but their secret is threatened when Jimmy witnesses an intimate moment between them. Meanwhile, Anna (recurring guest star SAMAIRE ARMSTRONG) announces that she is moving back to Pittsburgh. Convinced that her leaving is his fault, Seth races to the airport to stop her. ...

When actor Grady Bridges (COLIN HANKS
- " Orange County, Roswell") invites Summer & Marissa to his birthday party, the girls
...