Behind those tinted windows

“Grey’s Anatomy” has the elevator. “The Real World” has the confessional room. And “Gossip Girl” has the limousine. They are places where characters unburden themselves, out of the view of others. And because they’re not being watched, they sometimes behave as they otherwise might not; remove becomes a sort of enabler.

Earlier this season, Blair Waldorf (Leighton Meester) famously surrendered to the advances of grade-A cad Chuck Bass (Ed Westwick) in the back of a limo. Last week, Lily van der Woodsen (Kelly Rutherford) used hers as a mobile therapy space with both her daughter, Serena (Blake Lively), and her former boyfriend, Rufus Humphrey (Matthew Settle).

The limousine is a tantalizingly private space on a show in which so much happens in public, either on the actual streets of New York or disseminated via the Gossip Girl blog. But there’s just one thing: Only rich people have limos.

“Gossip Girl” (CW, Mondays at 8 p.m.) has spent most of the season experimenting with class miscegenation: Serena slumming it with boyfriend Dan Humphrey (Penn Badgley), and Dan’s sister Jenny (Taylor Momsen) trying desperately to climb the social ladder of the Upper East Side, where she and Dan attend school. The person who knows Blair the most intimately, who aids and abets her even when she’s doing wrong, is her maid Dorota (Zuzanna Szadkowski).

But the recent, post-writers strike episodes have been, gleefully, beginning to reinforce the wall between the haves and have-nots. After Blair was dethroned from her spot atop the social ladder after her dalliances with Chuck and Nate Archibald (Chace Crawford), Jenny took the train in from Brooklyn to fill her Louboutins. (Costume design, by Eric Daman, is spectacular, such as Chuck’s fluorescent trench coats and Jenny’s high-end DIY dresses; like Patricia Field’s work on “Sex and the City,” to which Daman also contributed, it is a hypertrophied version of New York that speaks as loudly as any character.)

Short-lived era

JENNY also inherited a gift for bitchiness and a gaggle of minions -- the new girls, Elise (Emma DeMar) and Hazel (Dreama Walker), are physically small, and their faces are packed disturbingly thick with makeup, in the manner of child pageant contestants. They too have grown up too soon.

When Blair returned to school, Jenny spilled yogurt on Blair’s head. But Jenny’s reign on the top was short -- later that episode, she was caught stealing a Valentino dress from the mother of a rich friend, leading to her meltdown. Momsen is an astute actress, far less wide-eyed than her character has been, and she played Jenny’s descent perfectly: “You think that you can just send me off to school with a plaid skirt and a Metro card and that everything will be OK,” she tells her father, Rufus, before storming out of the room.

In subsequent episodes, her relationship with preppy Asher (Jesse Swenson) is revealed to be a sham -- he is gay, and she is his beard. “You’re Jenny Humphrey from Brooklyn,” he tells her, icily. “You need status, access, resources. I give that to you.” But the relationship doesn’t end before Jenny and her friends display some dazzling shorthand, a testament to Jenny’s success at infiltrating her new world.

Hazel: Maybe Asher doesn’t like girls.

Jenny: Is that why we went dessert?

Elise: You went dessert?!?!?!

Jenny: No, he did.

Hazel: Well done. Make him work for it.

While Jenny tries to avoid getting shredded by polite society, her brother Dan has been largely quiet, because Serena has had to expend her energy battling with frenemy Georgina Sparks (Michelle Trachtenberg), her former buddy in all things Dionysian. Were Trachtenberg less robotic, it would have been clearer how Georgina entranced Serena so. But the snuff tape she has depicting Serena doing drugs with a young man who then overdoses seems small in comparison to her many crimes of friendship -- casually outing Serena’s brother Eric (Connor Paolo) at the Van der Woodsen dinner table, adopting another identity and befriending Dan in order to complicate Serena’s life.

At the end of last week’s episode, that ruse was about to be revealed, thanks to the combined efforts of Blair, Chuck and Nate, who have otherwise spent the bulk of this season in various states of conflict. There are some things the Upper East Side must do for itself, and getting rid of Georgina is one of those things. “What if I told you I knew where Georgina Sparks was right now?” Blair says to Chuck, her face flush as if she were in heat; revenge is her aphrodisiac.

Earlier, Nate, Chuck and Blair had to physically block Dan from climbing the staircase in the Waldorf home that would take him to Serena, who was doubled over in the bathroom after a night of guilt-driven excess. As ever, there are certain spaces Dan can never access. When Serena does come down to see Dan, she tells him, falsely, that she has cheated on him so that he will dump her -- better to put the wall back up than ask him to understand what life is truly like on the other side.

“Why do I get the feeling you’re actually enjoying this?” Nate asks Chuck, who coolly replies, “Call me sentimental.”