By Youyoung Lee
October 25, 2007 at 12:00 PM EDT

Unbeknownst to producers, last night’s Gossip Girl provided a quick lesson in Newton’s third law of motion. Yes, appearances can be deceiving, a point pounded into our heads by the Upper East Side’s most breathy blogger. But the episode’s real revelation is that, permitting the scientist’s theory that every action has an equal and opposite reaction, Serena and newbie Vanessa (played by the cheeky Jessica Szohr, left) are actually the same person.

Let’s examine the ways, shall we? Each girl sports an unruly, Harlequin-worthy mess of hair — though in opposite shades of the color spectrum. Both are epitomes their uptown/downtown environments: Alice and Olivia-favoring Serena dons sparkly sheaths found only north of Bryant Park, in the city’s most rarefied addresses, while Vanessa could be a walking advertisement for the Lower East Side’s main-staple retail store A-Life: gold hoops, neon jazzercise gear, and all. And each lady returns to New York after a mysterious disappearance, though to very different locales: the countryside in Vermont; boarding school. But where these modern day princess-and-the-pauper pair meet is in Dan (Penn Badgley, right). Both seek the young Humphrey’s company, cloying for his attention and approval; each girl, hopeless without him, feels slighted by the presence of the other.

Anyway, tensions were riding high at Blair’s Masquerade Ball, which appeared to be half high school prom, half Eyes Wide Shut swinger party. Homegirl finally gets a taste of her own medicine, realizing after Dan’s divided attention that the world does not revolve around her. Chuck, dressed like the devil he is, finds himself exactly where he wanted to be (half-naked, banging), albeit under different circumstances (alone, against the door). UES pledge Jenny, in her wobbly, yearning desire to be part of the crowd, earns and loses a diamond bracelet in a Guy de Maupassant-type twist. And Nate’s coke-sniffing father proves to be the most pathetic of the bunch — clamoring after Eleanor Waldorf’s clothing line, he brown-noses his way throughout the adult soirée, until finally the promise of his wife’s ungodly rock on her finger seals the deal. (What next? Turn into Rumpelstiltskin and pawn off his grandchildren?) Nate, more the victim of his circumstances rather than the product of it, watches on somberly, forced to confront his father’s hypocrisy only when Archibald the elder pegs the drug use on his own son. Oh, the audacity.

So point made, Gossip Girl: these “cases of mistaken identity, ironically not involving masks” occur beyond glamorous parties into behind closed doors. With or without secret pacts, not even the starchiest, stiffest white collar can help conceal our true colors. And if you just can’t wait until the next episode, read EW‘s Lindsay Soll’s interview with GG exec producer/writer Stephanie Savage for her reasons why Jenny isn’t a double-D chest in the show and other changes — plus a few spoilers.