SETH AND SUMMER HIT A DRY SPELL ON "THE O.C." THURSDAY, MARCH 23, ON FOX

When an old nemesis returns to Newport, Ryan gets caught up in helping her, causing a rift between him and Sadie. Seth and Summer are faced with a new problem that Taylor tries to solve. Meanwhile, Marissa finds herself all alone in Newport with no one to turn to and Sandy grapples with business pressure on "The Undertow" episode of THE O.C Thursday, March 23 (9:00-10:00 PM ET/PT) on FOX. (OC-318) (TV-14 L, S)

Cast: Peter Gallagher as Sandy Cohen, Benjamin McKenzie as Ryan Atwood, Adam Brody as Seth Cohen, Melinda Clarke as Julie Cooper, Mischa Barton as Marissa Cooper, Kelly Rowan as Kirsten Cohen, Rachel Bilson as Summer Roberts.

Guest Cast: Autumn Reeser as Taylor; Jeff Hephner as Matt Ramsey, Nikki Reed as Sadie; Cam Gigandet as Volchok, Nikki Griffin as Jess Sathers, Shaun Duke as Henry Griffin; and Matthew Cohen as Jim.