Having seriously dated for one week, Marissa & Ryan are progressing slowly. Summer (recurring guest star RACHEL BILSON) tries to deny her true feelings for Seth as she witnesses Anna (recurring guest star SAMAIRE ARMSTRONG) & Seth getting closer. Meanwhile, the case against Kirsten's father, Caleb (recurring guest star ALAN DALE), continues to cause friction between Sandy & Kirsten. & Julie (recurring guest star MELINDA CLARKE) tries to mend her relationship with Marissa, inviting her, Jimmy & Ryan to attend her charity event--where her new relationship is revealed. ...

When Seth tries to choose between dating Summer (recurring guest star RACHEL BILSON) or Anna (recurring guest star SAMAIRE ARMSTRONG), he ends up in the middle of a very complicated situation. Meanwhile, Ryan visits his brother, Trey (recurring guest star BRADLEY STRYKER), in prison, accompanied by Marissa. When Julie (recurring guest star MELINDA CLARKE) finds out that Marissa is with Ryan in Chino, she becomes furious. As everyone nervously waits at the Cohen house for Ryan & Marissa to return, tensions mount, making the holiday a Thanksgiving to remember. ...

After Thanksgiving, Anna (recurring guest star SAMAIRE ARMSTRONG) & Summer (recurring guest star RACHEL BILSON) remain upset with Seth for his behavior on the holiday, & Seth struggles to reconcile with them. Meanwhile, Julie (recurring guest star MELINDA CLARKE) has relationship problems of her own. Jimmy & Sandy team up to tackle Jimmy's legal issues. A secret indiscretion by Kirsten is exposed. Ryan & Luke become partners on a history project, & an astonishing revelation creates an unexpected alliance between them. ...

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 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. ...

Caleb (recurring guest star ALAN DALE) once again puts Kirsten in a difficult situation when he forces her to terminate Julie. After yet another crisis with Ryan, Sandy & Kirsten question their decision to bring him into their home. Meanwhile, Ryan & Luke become allies in their quest to protect Marissa from Oliver (recurring guest star TAYLOR HANDLEY). When Marissa discovers the truth about Oliver, a tense showdown ensues--and Sandy & Ryan must come to the rescue. ...

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. ...