MONDAY, AUGUST 4

"GOSSIP GIRL" � (8:00-9:00 p.m. ET)

"Desperately Seeking Serena" (TV-14, DLS) (HDTV)

MICHELLE TRACHTENBERG (�BUFFY THE VAMPIRE SLAYER�) GUEST STARS AS EVIL GEORGINA SPARKS IN A FOUR-EPISODE ARC � Serena�s Upper East Side world is turned upside down when her former partner in all things bad, Georgina Sparks (guest star Trachtenberg), returns to Manhattan to stir up trouble and Serena�s past. When Dan (Penn Badgley) notices that Serena seems preoccupied he jumps to the conclusion that it must have something to do with Serena�s new roomie and soon-to-be step-brother, Chuck (Ed Westwick). Nate (Chace Crawford) finds romance with the last person he was expecting to connect with, Vanessa (Jessica Szohr). Jenny (Taylor Momsen) meets a new guy, Asher Hornsby (guest star Jesse Swenson), who just might be her ticket to permanent popularity. Finally, Blair (Leighton Meester) hatches a secret plan to sabotage her biggest rival, Nelly Yuki (guest star Yin Chang). Matthew Settle also stars. The episode was directed by Michael Fields and written by Felicia D. Henderson (#114).