Georgina (guest star Michelle Trachtenberg, "17 Again") returns to the Upper East Side after undergoing a major transformation. Chuck (Ed Westwick) and Nate (Chace Crawford) find themselves at a major crossroads in their relationship as it pertains to their mutual interest in Blair (Leighton Meester). Serena (Blake Lively) finds her relationship with Gabriel (guest star Armie Hammer) growing more complicated.