"Serena deserves someone who would sacrifice anything to be with her," Nate yells, which... Is exactly what he just told Tripp not to be, so as usual Nate's thought processes are like totally inscrutable. Chuck says that the real secret is that Nate is so far gone that he actually stole from the Chuck Bass, and Nate feels bad, and Chuck blithely does his whole blithe Yoda wisdom thing that's frankly getting old about how Nate should just tell her how he feels or whatever. (Note: Nobody ever says this in real life, or means it, because it's absolutely dumbshit advice. If you know, you know, and you always know. Being a man doesn't mean making huge stupid gestures, because drama is always more about you than it is about me: If you know, you know. None of this "I have to just once tell you this or I will die." It's fake and childish.) Anyway, Nate is also wearing a rollneck sweater, I think, or hopefully a scarf, whatever, he looks great, and Chuck says S deserves to be with a guy who deserves to be with her or some such pointless nonsense.
Blair strums Rufus's abandoned guitars in Bart's old office, and S snorts that Lily probably hasn't even given R the vault combo, and Blair of all people says pithily, "Now that Bart's not around to keep files on everybody, maybe you guys don't need one?" She gets her passport thing, which is leather from the skin of a golden crocodile, and then Tripp appears. You can actually hear his Crazy Eyes echoing off the surfaces before you see him, like you are now a bat. Blair immediately threatens to judo chop him or something, and Tripp explains with tears in the Crazy Eyes that he just left Maureen for the fiftieth time today, but that the difference this time is that she's going to ruin his entire life for him, so that must mean he really loves Serena, so he's going to go downstairs and wait creepily for Serena to come join him for a week of whoredom in the country.
Blair, who is so consumed by reputation and standing that the very idea Tripp would willingly go there means that he really does care about S, gives an about-face on the issue of Tripp and tells S to follow her heart. Which, the way it's written is crappy, but the plotpoint is solid: Blair's not a staunch defender of marriage, she's just against being retarded, which is what S was doing, assuming that Tripp is like 99% of guys. But the fact that he just gave up the two things B loves most -- power and rep -- means he's being for real, so go for it. S ducklips about it for a bit, and then notices Carmen Sandiego's letter in the vault, and notices that A) it's postmarked like pre-Tripp era, and B) it's been opened.