MONDAY, APRIL 28

"GOSSIP GIRL" � (8:00-9:00 p.m. ET)

"Desperately Seeking Serena" (TV-) (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).