"Hot potato coming through. Hot tomato," a stage manager is barking as he shuttles equipment through the backstage area of the Studio at Webster Hall. It's 10 minutes before showtime and Sleigh Bells' Alexis Krauss, in a sheer bodysuit and spotless white Keds, is duct-taping mic equipment to her waist. Her bandmate, Derek Miller, wearing black Sambas and a gray INXS T-shirt, is opening a can of Bud Light. "Only the finest," he says.

Sleigh Bells has gone from tiny to huge in seemingly no time at all. Just last September they were the opening act for ...And You Will Know Us by the Trail of Dead, and maybe a dozen people stumbled into the Music Hall of Williamsburg early enough to see the Brooklyn duo tear through what was then their entire repertoire in 12 minutes. Six months later—the last time they played Webster Hall—Jay-Z and Beyoncé were rumored to be in attendance.

But tonight they're playing the modest-size Studio, a basement space beneath the more famous venue, as part of MTV's "Live in NYC" series, and the backstage area is a mess. A single halogen lamp lights the room, and the catering table is cluttered with beer cans, a platter of crudités (untouched), a bottle of Jameson (empty), a bottle of wine (empty), a loaf of bread (untouched), and a fruit plate (untouched). There is a rumor about pizza.

"God, I'm hot," Alexis says. She peels off her leather jacket and throws it on the couch next to her unzipped duffel bag of tricks: neon tops, leggings, a Ziploc baggie full of hoop earrings. Wandering in and out are Andrew Everding (Thursday), Ryan Primack (Poison the Well), Zeb and Shoaib Malik (POPO, the Philadelphia-based brother duo who opened tonight), and an unclaimed willowy brunette. Shoaib wears a mesh shirt over a tie-dyed tank top, which creates a moiré effect. "It looks like an oil spill," the willowy girl observes. "That's racist," Zeb says.

Merlin Bronques, the photographer from LastNightsParty, slithers backstage and tells Alexis to stand on a couch so that he can take photos of her.

"Five minutes?" says an MTV employee with a clipboard.

"Six minutes," says another MTV employee.

"Seven minutes?" says a third MTV employee.

Will, Sleigh Bells' co-manager and Derek's best friend, kicks Bronques out. "Who was that guy?" he mutters. "Miller. WHERE'S MILLER?" barks the same stage manager from before. Then he says to Will, "Did you really just sigh and roll your eyes at me?"

Miller—or, as I've known him since graduating college, Derek—is nervously bopping to TLC's "Creep," the last song on his mix before the band goes out. A couple of years ago, Derek, Will, and I were eating sandwiches under the elevated J/M/Z train when Derek mentioned he was looking for a girl singer to complete his new music project.

"Can you sing?" he asked me.

"Fuck no," I said.

That isn't false modesty, but rather an example of disaster averted: the baby carriage from movie chase scenes that gets struck by a car—gasp—and tin cans go flying all over the place (whew). Because what happened next is this: Derek met Alexis while waiting on her and her mom at a Brazilian restaurant, and the two proceeded to record some demo tracks, which were excellent. Then in August 2009, I blogged about the duo for a website coordinated by Spike Jonze for his movie Where the Wild Things Are. Spike got excited about the music and played it for his friend M.I.A., who also got excited. Several other things happened after that, and now here they are at the low-ceilinged Studio, about to play for a packed audience that's already generating a smell typically associated with the end of a show: booze, sweat, booze sweat. Ryan and Derek hug.

"I don't know what's gonna happen," Derek says. "Maybe nothing."

Or maybe the duo will launch into "Tell 'Em," the first single from Treats, and the floorboards will shake and the bass will be vigorous enough to send tingles up your feet. If you've ever been lightly tased, that's what it feels like.

Alexis oozes, flails, jumps, and skitters across the stage. Her outfit of skintight leggings, tank top, and those Keds is both practical (it facilitates movement) and seductive (ditto). "This is a dance song, so DANCE!" she yells before launching into "Kids." It's an assignment, not a suggestion—Alexis was a schoolteacher in the Bronx before she was Sleigh Bells—and the audience complies like a room of third-graders competing for extra credit.

During "Rill Rill," Derek ducks backstage to give Alexis the floor, the INXS shirt a wetter shade of gray. "I'm hot," he says, tugging on his jacket. "But I'm keeping this on. It makes me feel less insecure." He goes out again. "Derek knows he doesn't have to impress certain people because the sound is bigger than that," says Zeb, who is sitting on the couch with a beer. He takes a sip. "Also, I'm pregnant with his baby."

Derek and Alexis tumble backstage after ending with "Crown on the Ground," and Derek collapses on a chair next to Zeb, who drapes a hairy leg over him. "Zeb is beautiful inside and out," Derek says, patting the leg. He eats a handful of ice. Webster Hall's manager stops in to deliver another bottle of Jameson. Everyone takes a shot.

"Alexander Wang's assistant e-mailed me," Will is saying. "She was like, 'Can Alex come to the Philly show, plus seven?'"

"Plus seven?" someone asks. "Jesus. Do they pay for the tickets?"

"Well, sometimes they offer. But what it really means is 'Can you add me to the list?'"

Someone is smoking weed. Derek wants to know the score of the Saints game. He, Andrew, and Ryan are clustered around the Jameson bottle and they're talking in the way that men talk when they've known each other forever.

"Are you gonna barf?"

"No. That's illegal."

"What was Eddie Vedder's wife's maiden name again?"

Around midnight, Alexis, who is extremely sweet and wholesome offstage, leaves with her parents to go home. "Do we have a plan?" Derek asks. Someone suggests Soft Spot, a bar in Brooklyn, and the rest of the gang head out to load the van or keep drinking.

The fruit plate is untouched.

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