1. 'The Revengers," 6.09
After a run-in with an increasingly paranoid Bart (guest star Robert John Burke), Blair (Leighton Meester) grows alarmingly concerned for Chuck’s (Ed Westwick) safety. Wanting to make things better for Chuck, Blair devises a plan with the help of Serena (Blake Lively), Georgina (Michelle Trachtenberg) and Sage (Sofia Black-D’Elia) to try and get what they need out of Bart.