In Gossip Girl Season 6, Episode 5 “Monstrous Ball” (original air date November 12, 2012), the Upper East Side is getting ready for the big Cotillion Ball, and Blair Waldorf (Leighton Meester) is working hard at designing a gown to show the world that she can be a good head of Waldorf Designs… even after that snafu at her fashion show a few weeks ago. Dan Humphrey (Penn Badgley) is staying with her and sees the modest gown she was planning on using, but convinces her she needs to be edgier.
Meanwhile, there seems to be trouble in paradise for Serena van der Woodsen (Blake Lively) and Steven Spence (Barry Watson). Steven seems to be pre-occupied with something and has barely spoken to her all week. Sage (Sofia Black D’Elia) comes in carrying with a big poufy dress and says she’s ready for cotillion. Serena offers to help her prepare, but Sage rudely brushes it off. Steven invites Serena to go with them, and after she accepts, Sage remarks, “So much for me being the only teenager on my father’s night tonight.” Burn!
Serena goes to Nate Archibald (Chace Crawford) and asks if his gf Sage has said anything about why Steven is acting weird. He makes a joke about his exes going through his emails, giving Serena the idea to snoop. Back at Steven’s, she goes through his bag for clues and sees a diamond ring. She’s jumping up and down as Sage walks in, so she quickly puts in back in the bag and says how happy she is to attend her cotillion tonight. Once Serena leaves the room, Sage goes into Steven’s bag and sees the ring. She later confronts him about it, and he confirms he’s going to propose. But not if she has anything to do with it…
Serena goes to Lily (Kelly Rutherford) and tells her she thinks Steven is about to propose. That would explain why he called her this morning to meet. She says no matter what she says, she knows Serena will do what she wants.
Sage meets up with Blair and says she’s ready to work together. She says she’ll wear one of Blair’s Waldorf Design dresses if Blair will help her stall the proposal. It’s a deal! Blair calls Lily and expresses her concern about Steven and Serena getting married. She knows that Lily will do everything in her power to stop the relationship from going further if she has any doubt.
As Serena is getting her nails done so they’ll look great for the ring, she gets a text from Steven saying “Change of plans,” and that she shouldn’t go to the ball anymore. Then, immediately after, she sees a blast from Gossip Girl that includes a picture of Steven walking out of Harry Winston saying he went in with a ring, and came out without one.