Lily and Rufus decide to move up their wedding to the next day, but will someone or something come between them before they can become married? Chuck discovers a secret that Carter (recurring guest star Sebastian Stan) has been keeping from Serena. Dan and Vanessa are pulled into one of Georgina's (recurring guest star Michelle Trachtenberg) schemes. Blair is suspect of Bree (recurring guest star JoAnna Garcia) and shares her concerns with Nate. Musical group Sonic Youth performs.