The O.C. Goes N.Y.C.

It turned out also to be a favorite spot for Thoth, a street performer famous in his own right (and the subject of an Academy Award–winning short documentary), decked out in a gold loincloth, red feather headdress and not much else, who plays violin, sings falsetto soprano and shakes the bells around his ankles. An assistant director quietly spoke into his ear while Thoth sat on his knees, unyielding. In the darker corners of the underpass various homeless people slept on the concrete benches, untroubled.

“Why does it suddenly seem like we’re shooting a Fellini movie,” laughed producer Amy J. Kaufman, who seemed remarkably calm, given the circumstances. “When you work in New York you get used to the fact that things can change on you very suddenly, very dramatically, and there are some crazy parameters.” As if to illustrate her point, Thoth rose to his feet and took advantage of the crowd taking shelter from the storm and began a new performance. Ms. Kaufman sighed. “We have made an arrangement with … Thoth … he’s promised he’ll go away in 20 minutes. We’ve made other arrangements with the various people sleeping in various corners,” she said. “I think it’s actually a perfect example of the New York working spirit. It can end up being a fantastically beautiful scene—maybe even better than we originally conceived. Either way, it will be a great story to tell.”

If the actors knew that they might be merely weeks away from teen superstardom, they didn’t act like it. Mr. Crawford, light-eyed with impeccable bone structure, snapped his fingers and sang under his breath while waiting next to his TV dad. Not too far away at the makeup and hair trailer, Ms. Lively—a blonde who resembles a combination of a young Ellen Barkin and Kate Hudson with legs that go on to infinity—sat reading the script of her upcoming scene. Her dog, a caramel curly-haired ball of fluff wearing a collar dotted with rhinestone dog bones, ran wildly about dragging its leash behind him. “Mom,” Ms. Lively yelled in pitch-perfect teenager to her startlingly similar-looking mother. “Do you have the dog?”

“She’s been keeping me up nights,” faux-sighed her beaming-with-pride mother minutes later, explaining that the young actress had been anxious about shooting. Ms. Lively was the name Mr. Schwartz and Ms. Savage kept reading on fan sites talking about who they thought should play Serena; “Ninety-five percent of the time they’d say Blake Lively,” he said.

“Apparently I’m the only actress with long blond hair,” laughed Ms. Lively, now ready for her scene and clad in skinny lavender jeans and a somewhat questionable hat as she walked from trailer to set, a P.A. carefully holding an umbrella overhead. Next to her was Leighton Meester, decked out in pearls and red lipstick. The girls joked back and forth, breaking into song and teasing each other, acting both their and their characters’ ages. As they rounded the steps leading down to the fountain Ms. Lively stopped. “What is this? This is gorgeous!” She smiled at Ms. Meester and threw her arms wide as if to embrace the landscape. “Look at where we work!”