S1, E15: Serena's Upper East Side world is turned upside down when her former partner in all things bad, Georgina Sparks (recurring guest star MICHELLE TRACHTENBERG - "Buffy the Vampire Slayer," "Six Feet Under"), returns to Manhattan to stir up trouble -- and Serena's past. When Dan notices that Serena seems preoccupied, he jumps to the conclusion that it must have something to do with Serena's new roommate and soon-to-be stepbrother, Chuck. Meanwhile, Nate finds romance with the last person he was expecting to connect with, Vanessa, and Jenny meets a new guy, Asher Hornsby (recurring guest star JESSE SWENSON), who just might be her ticket to permanent popularity. Plus, Blair hatches a secret plan to sabotage her biggest rival, Nelly Yuki (guest star YIN CHANG - "Law & Order: Criminal Intent," "Six Degrees").