The summer is officially over, and it's the first day of school. Summer (recurring guest star RACHEL BILSON) still ignores Seth in public, but privately she is jealous of Seth's burgeoning relationship with iconoclastic East Coast girl Anna Stern (recurring guest star SAMAIRE ARMSTRONG). And Summer isn't the only person fighting feelings of jealousy. Kirsten still isn't comfortable with Sandy's friendship with his sexy new co-worker, Rachel (recurring guest star BONNIE SOMERVILLE). Rachel makes matters worse when she specifically enlists Sandy to work on a lawsuit that an environmental group has initiated against Kirsten's father and his land development company, despite the obvious conflict of interest. Kirsten is incensed, but conflicted Sandy truly believes in the environmentalists' cause.Meanwhile in school, Marissa and Ryan become closer, but Luke is still desperate to win her back. When it looks like Luke may succeed, Ryan lets his jealousy overwhelm his reason and starts a fight with Luke. Disappointed

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

Having seriously dated for one week, Marissa and 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) and Seth getting closer. Meanwhile, the case against Kirsten's father, Caleb (recurring guest star Alan Dale), continues to cause friction between Sandy and Kirsten. And Julie (recurring guest star Melinda Clarke) tries to mend her relationship with Marissa, inviting her, Jimmy and 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 and Marissa to return, tensions mount, making the holiday a Thanksgiving to remember.

Seth excitedly introduces a skeptical Ryan to Chrismukkah, a Cohen family tradition that resulted from Kirsten being Christian and 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) and Summer (recurring guest star Rachel Bilson), both of whom want to date him exclusively. Meanwhile, on opposing sides of a lawsuit, Sandy and Kirsten dread working through the holiday season, but Kirsten learns something about her father that could change everything. And Ryan and Marissa's shopping trip leads to trouble--and the beginning of even bigger problems for Marissa.

Matt Mitovich interviews Rachel Bilson about Jumper, Chuck, and The OC.

Rachel Bilson after shopping at Barneys New York.

Rob Huebel grills Jamie Bell and Rachel Bilson!

Michael (Zach Braff) confides his feelings to Kim (Rachel Bilson).