Michelle Trachtenberg

Georgina Sparks, Serena's former partner in all things bad, returns to Manhattan; Nate finds romance with Vanessa, the last person he would expect; Jenny meets a guy who could be her ticket to permanent popularity.

With Serena's life and reputation on the line, Blair -- as Serena's best friend -- decides to take matters into her own hands to deal with the manipulative and evil Georgina Sparks (recurring guest star Michelle Trachtenberg). Lily prepares for her wedding day, which is destined to be the Upper East Side's social event of the year, and finds that Rufus is never far from her thoughts. Serena finally opens up to Dan, pours out her heart and tells him the truth about her past, but will it prove to be too late to save their relationship? And Lily's interior decorator, Amelia (heiress and model Lydia Hearst), makes a big impression on Chuck.

Georgina (recurring guest star Michelle Trachtenberg) reveals the true reason that Serena fled Manhattan for boarding school, and Serena quickly falls back into her old habits. Blair, Nate and Chuck must put their complicated feelings for each other aside to help their friend. Unfortunately, Serena is too ashamed to share the truth with Dan, leaving him to assume the worst about his girlfriend. Meanwhile, Rufus is thrilled when his band is invited to perform at a Rolling Stone-sponsored concert, but Lily is the last person he expects to see at the performance, especially since her wedding rehearsal dinner is the same night. Recording artist Lisa Loeb and famous cake designer Sylvia Weinstock appear as themselves.

Georgina (recurring guest star Michelle Trachtenberg) informs Serena that she is prepared to reveal damaging information from Serena's past, but no one is ready for what Georgina does next. Blair and Jenny escalate their "popularity war" by spreading scandalous rumors about each other through Gossip Girl. Dan witnesses Jenny's new boyfriend, Asher (recurring guest star Jesse Swenson), cheating on her, but Jenny refuses to listen to her brother's warning. Rufus goes to Lily for advice on how to handle Jenny's recent out-of-character behavior. Plus, one of the Upper East Side teens reveals that he is gay.

Melinda (guest star Michelle Trachtenberg), a rebellious teenage girl who is immunocompromised as a result of medications she’s taking after a heart transplant, has a severe allergic reaction and goes into shock despite living in a "clean" room. House and the team step in to figure out exactly what caused the reaction, but end up playing referee between Melinda, her overprotective mother (guest star Mel Harris) and her boyfriend.