S6, E7: Serena and Dan realize that they need to make amends with the people they have wronged. Blair has one last chance to prove to her mother her worth as a fashion designer and, with Serena's help, comes up with a plan to make her line the "it" look for Sage (recurring guest star SOFIA BLACK-D'ELIA) and her friends. Meanwhile, Chuck is close to getting the evidence he needs against his father, until one of his closest allies reveals his plan to Bart (recurring guest star ROBERT JOHN BURKE). Recurring guest stars MICHELLE TRACHTENBERG and WILLIAM BALDWIN appear as Georgina Sparks and William van der Woodsen, respectively.