After Eleanor (guest star Margaret Colin) gives Blair an ultimatum, Blair is even more determined to remedy Waldorf Designs’ problems by making a splash with a dress at the upcoming Cotillion, but a shocking revelation at the ball affects everyone. Serena (Blake Lively) becomes worried about Steven’s (guest star Barry Watson) attitude toward her, but after some investigating she discovers the surprising reason why. Chuck (Ed Westwick) finds an unlikely ally as he tries to drive a wedge between Bart (Robert John Burke) and Lily’s (Kelly Rutherford) relationship to help expose his father’s secret.  Meanwhile, Dan (Penn Badgley) publishes another article, but the effect is just the opposite of what he was hoping for.