Meanwhile, Kirsten attends rehab in an attempt to put her life back together, while her husband Sandy assumes leadership of the Newport Group after Caleb's death and finds himself the heir-apparent to a legacy of scandal.

Marissa spirals out of control after her younger sister Kaitlin causes trouble on her return home from boarding school.

Sandy, Seth and Summer find a way to blackmail Dean Hess into letting Ryan back into Harbor.

The executive producers were series creator Josh Schwartz, McG, a co-founder of Wonderland, and Bob DeLaurentis.

Mischa Barton as Marissa, Rachel Bilson as Summer, Adam Brody as Seth, Melinda Clarke as Julie, Peter Gallagher as Sandy, Benjamin McKenzie as Ryan, and Kelly Rowan as Kirsten all returned to the main cast.

[36] Logan Marshall-Green returned for the season premiere, portraying Trey Atwood, comatosed as a result of the shooting in the second-season finale.

[36] Additionally Navi Rawat, Samaire Armstrong, Daphne Ashbrook and Nikki Griffin all made brief returns to guest star as Theresa Diaz,[37] Anna Stern,[37] Dawn Atwood,[38] and Jess Sathers,[39] respectively.

Willa Holland took over from Shailene Woodley in portraying Marissa's younger sister Kaitlin, who returns to the show after being away at boarding school last year.

[34] Cast member Michael Nouri continued as Summer's dad, Dr. Neil Roberts, who became a larger part of the series.

), Michael Cassidy (Zach), Shannon Lucio (Lindsay), Olivia Wilde (Alex), Billy Campbell (Carter), Kim Delaney (Rebecca), Johnny Messner (Lance), Kathleen York (Renee), and Marguerite Moreau (Reed).

[43] Jeri Ryan and Jeff Hephner also joined the cast to portray new adult characters Charlotte Morgan, a mysterious woman Kirsten befriends in rehab,[35] and Matt Ramsey, an overzealous business partner working at the Newport Group.

[44] New guest stars in recurring roles included Paula Trickey as Taylor's mother, Veronica Townsend; Erin Foster as a Newport Union student called Heather; Kayla Ewell and Nikki Reed as Johnny's girlfriend, Casey, and cousin Sadie;[45] Eric Mabius as new Dean of Discipline, Jack Hess;[46] Shaun Duke as Henry Griffin, head of the board at Newport Hospital; and Morena Baccarin as Griffin's daughter Maya.

As well as every episode from the season, the DVD release features bonus material including a gag reel, featurettes, and the making of a music video by The Subways.