While the Princess Bride prepares for her big day, the priest discusses with Chuck his plans to ruin it. And Georgina Sparks, who intends to join forces with the "world's biggest wedding crasher," has her own spoiler plot to put into action.
First in the day's well-heeled festivities is a brunch at Serena's. When the wedding planner announces Serena's escort's flight from Italy has been delayed, Dan steps in to be her dance partner. Earlier he told his father that as soon as Blair weds, he and Serena can quit pretending they're a thing again. When Blair arrives, she takes a moment with her BFF to talk about her pre-nuptials jitters. When she finds out that Serena hasn't told Dan that Blair said they could quit pretending, she advices Serena to just tell Dan how she feels already. Serena insists that there's nothing to tell.
As the priest and Chuck wrap up their breakfast, the priest suddenly falls ill. Chuck confesses he poisoned him in order to stop him from ruining the wedding. Just because he loves Blair doesn't mean he wants to ruin her life. He's not that kind of guy anymore. But later, Georgina meets up with the priest and gives him some pills for his nausea. She proposes to help him follow through with his scheme. He gives her an altar boy costume, thus granting the vengeful girl admission to the Wedding of the Century.
As Blair's nerves grow increasingly frayed, her mother tries to help calm her. Next thing, Mrs. Waldorf shows up at Chuck's flat to tell him she thinks Blair's making a mistake and she wants him to help her stop this thing.
Georgina's trying everything to stop it, too. Planning to seduce the prince in a backroom chamber of the church, she changes out of her altar-boy costume and into a slip. But she's caught before the prince comes into the room. She escapes through a side door to witness Chuck standing with Blair in her chamber trying to convince her to run away with him. Blair turns him down, saying she loves him more than anything, but even if she weren't with Louis, she couldn't be with him. She's only trying to do what's best for him. Serena comes in to tell her it's photo time. Georgina walks in after Blair and Serena leave, and tells him she recorded the whole thing. She gives Chuck her camera and leaves just before security comes to escort her out.
Alone with Blair, Serena tries to convince her to follow her heart, nevermind the pact she made with God to save Chuck's life after the accident. Blair won't listen and heads down the aisle, so Serena runs off to tell Chuck about Blair's religious superstitions. Meanwhile, Blair's proclamation of love to Chuck is already up on Gossip Girl and everyone can see the video on their phones while the ceremony begins. Chuck appears in a doorway hoping to entice Blair, but she goes through with the wedding anyway.
When Louis finds out about the video, he's finally finished with Blair. Meanwhile, Blair puts in a rescue call … to Dan, not Chuck, like you might expect. Everyone suspects Chuck was the one to upload the video to GG, but when we see Georgina upload a follow-up article, we're left wondering if she's been GG all along.