Blair and Chuck attack Serena and ask what the big idea is, and she explains the CLUES and how they've been sabotaging Carter's chances with her: The girl, the '95 Dom -- which S knows is B's favorite -- and the whole thing. "So we started a stealth campaign to destroy his credibility," Chuck says expansively. "Room service bill, the girl on the street..." Blair mentions a warrant they don't even know about yet, and suggests that Carter take a DNA sample down to the 24th precinct tomorrow. B swears she did it to save Serena, and Chuck says he just did it because he hates Carter. "All Carter cares about is himself. When we ran him out of town six months ago, he traded his Dubai ticket for Greece."
Remember, he was turning Blair all evil and Serena bought him a ticket out of the country with that Rhodes look in her eye? Well apparently what happened next is that Carter went to Greece and, per Chuck, "Spent the next few months checking in and out of every resort and hotel from there to Fiji." And now he's back, because he's broke. Serena realizes that in fact she is the mystery culprit after all, like some kind of Phillip K. Dick novel, and finally explains WHAT HAPPENED IN SANTORINI: Carmen Sandiego, aka Keith vdDubs, was supposed to be getting married two years ago. (Huh? Right about the time her brother was committing suicide and she was coming back to the UES? Did I skip a year in there? Retroactive continuity is a harsh mistress. This is like the Final Five thing all over again.)
So Serena asked Carter to help, secretly, and he said he had "access" to a boat. Which is why they got arrested, which is the only thing we already knew about WHAT HAPPENED, and so what Serena didn't know is that he's been looking for Keith this whole time, including when they ran him out of town last time. "And did he find him?" they ask, and she gets that look and takes off with the painting. B shoots Chuck a look and he calls his "guy at the precinct," and of all people, who should be listening, with a gimlet and attentive eye, but Bree Buckley. Of course, at this point I thought it meant that Keith was supposed to marry her sister-cousin, because that's still the only thing we know about her, but it turns out she wasn't listening for vdDubs news, but for Carter's name.
Look Homeward, Angel: "Which of us has known his brother? Which of us has looked into his father's heart? Which of us has not remained forever prison-pent? Which of us is not forever a stranger and alone?"