Pop-music purists invariably tell the same story about their favorite music. Whatever the genre—R. & B., classic punk, dance-hall reggae, Celtic lullabies—a purist will say that it was better at its inception, when the sound was an expression of something local and unique, before the terrible money came, and strangers corrupted the music with their embrace.

The purists are not entirely wrong. When a new sound sprouts on pop’s tree, invisible to passersby, it is a wondrous thing. But what happens next is often more interesting: the music begins to find an audience, record companies offer to pay musicians to make their sounds, and someone gives those sounds a name. The music is now a genre, and it grows willy-nilly, borrowing from other genres, which it may eventually resemble, while announcing itself as something you’ve never heard before.

Electronica and crunk passed through this stage not long ago, and grime, a British genre, has now entered it. Grime emerged from the rave culture of the late nineteen-nineties, and will sound to most Americans like hip-hop performed by m.c.s with English accents and really fast raps. Hip-hop, even at its harshest, is dance music. By contrast, grime sounds as if it had been made for a boxing gym, one where the fighters have a lot of punching to do but not much room to move.

In the past three years, grime producers (who make the beats that m.c.s rhyme over) have developed a fierce, antic sound by distilling the polyrhythms of drum and bass or garage—the music of choice at many raves—to a minimal style sometimes consisting of nothing more than a queasy bass line and a single, clipped video-game squawk. Today, the music’s choppy, off-center rhythms are blanketing London. Some tracks are beginning to show the influence of American hip-hop genres like crunk, but the m.c.s’ cadences are unmistakably black and British, indebted to Jamaican dance-hall music and West Indian patois.

Grime exists largely in an informal economy. Some artists make their débuts on homemade DVDs, which feature shaky footage of competitions between m.c.s—a little like spelling bees, but louder. Some of the most popular battles are filmed in a long, narrow basement in Leytonstone, at the home of Jammer, a producer who runs Jahmek the World, a respected independent label. The DVDs, with names like “Lord of the Mics” and “Eskimo Dance,” are sold in barbershops and record stores around London; pirate radio stations like Raw UK and Rinse FM broadcast tracks made days earlier; and, on cable, Channel U plays videos, including crude productions shot with handheld digital video cameras.

The grime artist Americans know best is Dizzee Rascal, a twenty-yearold from Bow, a working-class neighborhood in East London, where many grime artists live. Dizzee and his mentor, Wiley, who created one of the first grime tracks, “Eskimo,” have both released albums in the United States in the past year. And both appear on “Run the Road,” a new compilation that documents the genre’s industry and energy.

“Destruction VIP,” the most hopped-up track on the album, was produced by Jammer. It begins with a sample from what could be the soundtrack to a chase scene from a nineteen-sixties British police caper. Then Wiley leaps in, chattering taunts at his imitators: “I know hungry—he said he don’t know you. I know who’s who, and who’s who don’t know you.” The music Ping-Pongs between half time and a faster tempo, segueing into the next verse, which is performed by Kano, a young m.c. who enunciates calmly over the aggressive beat. The song—essentially a succession of boasts and threats to rivals—is a cab ride over piles of rebar, but Kano never spills his drink.

There isn’t a bad song on “Run the Road,” and several m.c.s—all still in their teens—stand out: Kano; Louise Harman, who goes by the name Lady Sovereign; and Ears, who is only seventeen but is apparently already feeling old. In the opening of a nostalgic song called “Happy Dayz,” he sings, “Do you remember that? Back in the days, when man was just bare happy? No worries, nothing to worry about? Those days were live, I miss them days, man.” When the world turns this fast, middle age comes early.

Kano, who has been releasing songs since he was sixteen, is featured on four of the sixteen tracks on “Run the Road.” Americans who are put off by British accents and grime slang like “nekkle” (great, very cool) and “bare” (lots of, many) will warm to Kano. His delivery on the song “P’s and Q’s,” a comically fastidious call to arms, is so composed that it is almost polite, even when he’s rhyming in double time: “This year’s gotta be mine, I’m the first in line. Wow, you got your first rewind, but the second line sounded like the first line. I ain’t got punch lines, I’ve got kick lines, and they ain’t commercial, but I’ve got hit lines.”

Lady Sovereign is not grime’s only female m.c.; others include Lady Fury, the brilliant No Lay, and an up-and-coming producer called Mizz Beats. But she is the scene’s sole white woman, and she seems destined to be its biggest success. The United States has yet to produce a universally accepted white female rapper, and there’s already a debate over Sovereign’s authenticity, even though she grew up in the same kind of public-housing project—Chalk Hill estate, now demolished—that many grime artists did. Besides, she’s good: pithy, clever, and able to use her honking voice to humorous effect, much like Eminem, to whom she has already been compared. There’s a hyperactive track on “Run the Road” called “Cha Ching (Cheque 1, 2 Remix),” which features as much hooting as rhyming, and nicely showcases her eccentric talent.

When I visited Sovereign in October, she and her producer, a man named Gabriel who goes professionally by Medasyn, were bunkered in a converted textile factory in East London, an appropriately filthy building where Medasyn rents studio space. Sovereign was curled up in an armchair, looking smaller and younger than eighteen. To her displeasure, people often point out that she looks like Sporty Spice, of the Spice Girls. Her hair was held up in a topknot and she wore a tracksuit. She spoke in a quiet, nasal voice, with the hedged courage of a teen-ager determined to take on the world every time she walks out the door.

After a few minutes of polite chat, she summed herself up: “I’m cheeky. I don’t tell stories and moan about.” Last July, she was signed by Island Records, a major label, but she still posts photographs of herself on Internet bulletin boards. (Medasyn told me that after Paris Hilton’s cell phone got hacked Sovereign “was one of the first people to get the numbers. She even phoned Christina Aguilera.”)

The day I stopped by, Sovereign and Medasyn played “Random” for me, a work-in-progress that captured grime’s most irrational, fractal qualities: a pair of palsied bass notes here, a fibrillating shaker noise there, and a wobbly melody line that didn’t sound entirely well. Sovereign began the song by quoting “Tipsy,” an American hip-hop hit, and coursed through a series of seemingly unrelated ideas: “I can’t see straight like I got one eye. Ooh (pop!). Your bottle’s open, oh my. Let’s get it started, move your arms around like fucked-up karate. . . . J. Lo’s got a body, you can’t see mine ’cause I wear my trousers baggy.”

When the song was over, Sovereign asked me if I thought grime would take off in America. Five months later, the answer is increasingly clear. “Pow,” a song by an m.c. called Lethal B, and grime’s biggest hit to date, has made its way to New York, where it is currently being played on Hot 97 by the influential d.j. Funkmaster Flex. The American m.c.s Stat Quo and Pitbull have already recorded new verses for the track.

This week, Lady Sovereign’s “Random” will be formally released as a single in London. The song was ultimately completed by a pair of producers called Menta, who gave Sovereign’s charming non sequiturs a danceable makeover. This version of “Random” combines grime’s squeaky bullets of noise with hip-hop’s more forgiving swing. Sovereign might see the song’s transformation as an auspicious portent. Grime is becoming familiar, a fine black mist dissolving in the air around us. ♦