S1, E18: 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.