he house at 1212 1/2 West Front Street in Plainfield, N.J., is a conventional midcentury home with slate-gray siding, white trim and Victorian lines. When I stood in front of it on a breezy day in October, I could hear the cries of children from the playground of an elementary school around the corner. American flags fluttered from porches and windows. The neighborhood is a leafy, middle-class Anytown. The house is set back off the street, near two convenience stores and a gift shop. On the door of Superior Supermarket was pasted a sign issued by the Plainfield police: ''Safe neighborhoods save lives.'' The store's manager, who refused to tell me his name, said he never noticed anything unusual about the house, and never heard anything. But David Miranda, the young man behind the counter of Westside Convenience, told me he saw girls from the house roughly once a week. ''They came in to buy candy and soda, then went back to the house,'' he said. The same girls rarely came twice, and they were all very young, Miranda said. They never asked for anything beyond what they were purchasing; they certainly never asked for help. Cars drove up to the house all day; nice cars, all kinds of cars. Dozens of men came and went. ''But no one here knew what was really going on,'' Miranda said. And no one ever asked.

On a tip, the Plainfield police raided the house in February 2002, expecting to find illegal aliens working an underground brothel. What the police found were four girls between the ages of 14 and 17. They were all Mexican nationals without documentation. But they weren't prostitutes; they were sex slaves. The distinction is important: these girls weren't working for profit or a paycheck. They were captives to the traffickers and keepers who controlled their every move. ''I consider myself hardened,'' Mark J. Kelly, now a special agent with Immigration and Customs Enforcement (the largest investigative arm of the Department of Homeland Security), told me recently. ''I spent time in the Marine Corps. But seeing some of the stuff I saw, then heard about, from those girls was a difficult, eye-opening experience.''

The police found a squalid, land-based equivalent of a 19th-century slave ship, with rancid, doorless bathrooms; bare, putrid mattresses; and a stash of penicillin, ''morning after'' pills and misoprostol, an antiulcer medication that can induce abortion. The girls were pale, exhausted and malnourished.

It turned out that 1212 1/2 West Front Street was one of what law-enforcement officials say are dozens of active stash houses and apartments in the New York metropolitan area -- mirroring hundreds more in other major cities like Los Angeles, Atlanta and Chicago -- where under-age girls and young women from dozens of countries are trafficked and held captive. Most of them -- whether they started out in Eastern Europe or Latin America -- are taken to the United States through Mexico. Some of them have been baited by promises of legitimate jobs and a better life in America; many have been abducted; others have been bought from or abandoned by their impoverished families.

Because of the porousness of the U.S.-Mexico border and the criminal networks that traverse it, the towns and cities along that border have become the main staging area in an illicit and barbaric industry, whose ''products'' are women and girls. On both sides of the border, they are rented out for sex for as little as 15 minutes at a time, dozens of times a day. Sometimes they are sold outright to other traffickers and sex rings, victims and experts say. These sex slaves earn no money, there is nothing voluntary about what they do and if they try to escape they are often beaten and sometimes killed.

Last September, in a speech before the United Nations General Assembly, President Bush named sex trafficking as ''a special evil,'' a multibillion-dollar ''underground of brutality and lonely fear,'' a global scourge alongside the AIDS epidemic. Influenced by a coalition of religious organizations, the Bush administration has pushed international action on the global sex trade. The president declared at the U.N. that ''those who create these victims and profit from their suffering must be severely punished'' and that ''those who patronize this industry debase themselves and deepen the misery of others. And governments that tolerate this trade are tolerating a form of slavery.''

Under the Trafficking Victims Protection Act of 2000 -- the first U.S. law to recognize that people trafficked against their will are victims of a crime, not illegal aliens -- the U.S. government rates other countries' records on human trafficking and can apply economic sanctions on those that aren't making efforts to improve them. Another piece of legislation, the Protect Act, which Bush signed into law last year, makes it a crime for any person to enter the U.S., or for any citizen to travel abroad, for the purpose of sex tourism involving children. The sentences are severe: up to 30 years' imprisonment for each offense.

The thrust of the president's U.N. speech and the scope of the laws passed here to address the sex-trafficking epidemic might suggest that this is a global problem but not particularly an American one. In reality, little has been done to document sex trafficking in this country. In dozens of interviews I conducted with former sex slaves, madams, government and law-enforcement officials and anti-sex-trade activists for more than four months in Eastern Europe, Mexico and the United States, the details and breadth of this sordid trade in the U.S. came to light.

In fact, the United States has become a major importer of sex slaves. Last year, the C.I.A. estimated that between 18,000 and 20,000 people are trafficked annually into the United States. The government has not studied how many of these are victims of sex traffickers, but Kevin Bales, president of Free the Slaves, America's largest anti-slavery organization, says that the number is at least 10,000 a year. John Miller, the State Department's director of the Office to Monitor and Combat Trafficking in Persons, conceded: ''That figure could be low. What we know is that the number is huge.'' Bales estimates that there are 30,000 to 50,000 sex slaves in captivity in the United States at any given time. Laura Lederer, a senior State Department adviser on trafficking, told me, ''We're not finding victims in the United States because we're not looking for them.''

ABDUCTION

In Eastern European capitals like Kiev and Moscow, dozens of sex-trafficking rings advertise nanny positions in the United States in local newspapers; others claim to be scouting for models and actresses. In Chisinau, the capital of the former Soviet republic of Moldova -- the poorest country in Europe and the one experts say is most heavily culled by traffickers for young women -- I saw a billboard with a fresh-faced, smiling young woman beckoning girls to waitress positions in Paris. But of course there are no waitress positions and no ''Paris.'' Some of these young women are actually tricked into paying their own travel expenses -- typically around $3,000 -- as a down payment on what they expect to be bright, prosperous futures, only to find themselves kept prisoner in Mexico before being moved to the United States and sold into sexual bondage there.

The Eastern European trafficking operations, from entrapment to transport, tend to be well-oiled monoethnic machines. One notorious Ukrainian ring, which has since been broken up, was run by Tetyana Komisaruk and Serge Mezheritsky. One of their last transactions, according to Daniel Saunders, an assistant U.S. attorney in Los Angeles, took place in late June 2000 at the Hard Rock Cafe in Tijuana. Around dinnertime, a buyer named Gordey Vinitsky walked in. He was followed shortly after by Komisaruk's husband, Valery, who led Vinitsky out to the parking lot and to a waiting van. Inside the van were six Ukrainian women in their late teens and early 20's. They had been promised jobs as models and baby sitters in the glamorous United States, and they probably had no idea why they were sitting in a van in a backwater like Tijuana in the early evening. Vinitsky pointed into the van at two of the women and said he'd take them for $10,000 each. Valery drove the young women to a gated villa 20 minutes away in Rosarito, a Mexican honky-tonk tourist trap in Baja California. They were kept there until July 4, when they were delivered to San Diego by boat and distributed to their buyers, including Vinitsky, who claimed his two ''purchases.'' The Komisaruks, Mezheritsky and Vinitsky were caught in May 2001 and are serving long sentences in U.S. federal prison.

In October, I met Nicole, a young Russian woman who had been trafficked into Mexico by a different network. ''I wanted to get out of Moscow, and they told me the Mexican border was like a freeway,'' said Nicole, who is now 25. We were sitting at a cafe on the Sunset Strip in Los Angeles, and she was telling me the story of her narrow escape from sex slavery -- she was taken by immigration officers when her traffickers were trying to smuggle her over the border from Tijuana. She still seemed fearful of being discovered by the trafficking ring and didn't want even her initials to appear in print. (Nicole is a name she adopted after coming to the U.S.)

Two years ago, afraid for her life after her boyfriend was gunned down in Moscow in an organized-crime-related shootout, she found herself across a cafe table in Moscow from a man named Alex, who explained how he could save her by smuggling her into the U.S. Once she agreed, Nicole said, Alex told her that if she didn't show up at the airport, '''I'll find you and cut your head off.' Russians do not play around. In Moscow you can get a bullet in your head just for fun.''

Donna M. Hughes, a professor of women's studies at the University of Rhode Island and an expert on sex trafficking, says that prostitution barely existed 12 years ago in the Soviet Union. ''It was suppressed by political structures. All the women had jobs.'' But in the first years after the collapse of Soviet Communism, poverty in the former Soviet states soared. Young women -- many of them college-educated and married -- became easy believers in Hollywood-generated images of swaying palm trees in L.A. ''A few of them have an idea that prostitution might be involved,'' Hughes says. ''But their idea of prostitution is 'Pretty Woman,' which is one of the most popular films in Ukraine and Russia. They're thinking, This may not be so bad.''

The girls' first contacts are usually with what appear to be legitimate travel agencies. According to prosecutors, the Komisaruk/Mezheritsky ring in Ukraine worked with two such agencies in Kiev, Art Life International and Svit Tours. The helpful agents at Svit and Art Life explained to the girls that the best way to get into the U.S. was through Mexico, which they portrayed as a short walk or boat ride from the American dream. Oblivious and full of hope, the girls get on planes to Europe and then on to Mexico.

Every day, flights from Paris, London and Amsterdam arrive at Mexico City's international airport carrying groups of these girls, sometimes as many as seven at a time, according to two Mexico City immigration officers I spoke with (and who asked to remain anonymous). One of them told me that officials at the airport -- who cooperate with Mexico's federal preventive police (P.F.P.) -- work with the traffickers and ''direct airlines to park at certain gates. Officials go to the aircraft. They know the seat numbers. While passengers come off, they take the girls to an office, where officials will 'process' them.''

Magdalena Carral, Mexico's commissioner of the National Institute of Migration, the government agency that controls migration issues at all airports, seaports and land entries into Mexico, told me: ''Everything happens at the airport. We are giving a big fight to have better control of the airport. Corruption does not leave tracks, and sometimes we cannot track it. Six months ago we changed the three main officials at the airport. But it's a daily fight. These networks are very powerful and dangerous.''

ut Mexico is not merely a way station en route to the U.S. for third-country traffickers, like the Eastern European rings. It is also a vast source of even younger and more cheaply acquired girls for sexual servitude in the United States. While European traffickers tend to dupe their victims into boarding one-way flights to Mexico to their own captivity, Mexican traffickers rely on the charm and brute force of ''Los Lenones,'' tightly organized associations of pimps, according to Roberto Caballero, an officer with the P.F.P. Although hundreds of ''popcorn traffickers'' -- individuals who take control of one or two girls -- work the margins, Caballero said, at least 15 major trafficking organizations and 120 associated factions tracked by the P.F.P. operate as wholesalers: collecting human merchandise and taking orders from safe houses and brothels in the major sex-trafficking hubs in New York, Los Angeles, Atlanta and Chicago.

Like the Sicilian Mafia, Los Lenones are based on family hierarchies, Caballero explained. The father controls the organization and the money, while the sons and their male cousins hunt, kidnap and entrap victims. The boys leave school at 12 and are given one or two girls their age to rape and pimp out to begin their training, which emphasizes the arts of kidnapping and seduction. Throughout the rural and suburban towns from southern Mexico to the U.S. border, along what traffickers call the Via Lactea, or Milky Way, the agents of Los Lenones troll the bus stations and factories and school dances where under-age girls gather, work and socialize. They first ply the girls like prospective lovers, buying them meals and desserts, promising affection and then marriage. Then the men describe rumors they've heard about America, about the promise of jobs and schools. Sometimes the girls are easy prey. Most of them already dream of El Norte. But the theater often ends as soon as the agent has the girl alone, when he beats her, drugs her or simply forces her into a waiting car.

The majority of Los Lenones -- 80 percent of them, Caballero says -- are based in Tenancingo, a charmless suburb an hour's drive south of Mexico City. Before I left Mexico City for Tenancingo in October, I was warned by Mexican and U.S. officials that the traffickers there are protected by the local police, and that the town is designed to discourage outsiders, with mazelike streets and only two closely watched entrances. The last time the federal police went there to investigate the disappearance of a local girl, their vehicle was surrounded, and the officers were intimidated into leaving. I traveled in a bulletproof Suburban with well-armed federales and an Immigration and Customs Enforcement agent.

On the way, we stopped at a gas station, where I met the parents of a girl from Tenancingo who was reportedly abducted in August 2000. The girl, Suri, is now 20. Her mother told me that there were witnesses who saw her being forced into a car on the way home from work at a local factory. No one called the police. Suri's mother recited the names of daughters of a number of her friends who have also been taken: ''Minerva, Sylvia, Carmen,'' she said in a monotone, as if the list went on and on.

Just two days earlier, her parents heard from Suri (they call her by her nickname) for the first time since she disappeared. ''She's in Queens, New York,'' the mother told me breathlessly. ''She said she was being kept in a house watched by Colombians. She said they take her by car every day to work in a brothel. I was crying on the phone, 'When are you coming back, when are you coming back?' '' The mother looked at me helplessly; the father stared blankly into the distance. Then the mother sobered. ''My daughter said: 'I'm too far away. I don't know when I'm coming back.''' Before she hung up, Suri told her mother: ''Don't cry. I'll escape soon. And don't talk to anyone.''

Sex-trafficking victims widely believe that if they talk, they or someone they love will be killed. And their fear is not unfounded, since the tentacles of the trafficking rings reach back into the girls' hometowns, and local law enforcement is often complicit in the sex trade.

One officer in the P.F.P.'s anti-trafficking division told me that 10 high-level officials in the state of Sonora share a $200,000 weekly payoff from traffickers, a gargantuan sum of money for Mexico. The officer told me with a frozen smile that he was powerless to do anything about it.

''Some officials are not only on the organization's payroll, they are key players in the organization,'' an official at the U.S. Embassy in Mexico City told me. ''Corruption is the most important reason these networks are so successful.''

Nicolas Suarez, the P.F.P.'s coordinator of intelligence, sounded fatalistic about corruption when I spoke to him in Mexico City in September. ''We have that cancer, corruption,'' he told me with a shrug. ''But it exists in every country. In every house there is a devil.''

The U.S. Embassy official told me: ''Mexican officials see sex trafficking as a U.S. problem. If there wasn't such a large demand, then people -- trafficking victims and migrants alike -- wouldn't be going up there.''

When I asked Magdalena Carral, the Mexican commissioner of migration, about these accusations, she said that she didn't know anything about Los Lenones or sex trafficking in Tenancingo. But she conceded: ''There is an investigation against some officials accused of cooperating with these trafficking networks nationwide. Sonora is one of those places.'' She added, ''We are determined not to allow any kind of corruption in this administration, not the smallest kind.''

Gary Haugen, president of the International Justice Mission, an organization based in Arlington, Va., that fights sexual exploitation in South Asia and Southeast Asia, says: ''Sex trafficking isn't a poverty issue but a law-enforcement issue. You can only carry out this trade at significant levels with the cooperation of local law enforcement. In the developing world the police are not seen as a solution for anything. You don't run to the police; you run from the police.''

BREAKING THE GIRLS IN

Once the Mexican traffickers abduct or seduce the women and young girls, it's not other men who first indoctrinate them into sexual slavery but other women. The victims and officials I spoke to all emphasized this fact as crucial to the trafficking rings' success. ''Women are the principals,'' Caballero, the Mexican federal preventive police officer, told me. ''The victims are put under the influence of the mothers, who handle them and beat them. Then they give the girls to the men to beat and rape into submission.'' Traffickers understand that because women can more easily gain the trust of young girls, they can more easily crush them. ''Men are the customers and controllers, but within most trafficking organizations themselves, women are the operators,'' Haugen says. ''Women are the ones who exert violent force and psychological torture.''

This mirrors the tactics of the Eastern European rings. ''Mexican pimps have learned a lot from European traffickers,'' said Claudia, a former prostitute and madam in her late 40's, whom I met in Tepito, Mexico City's vast and lethal ghetto. ''The Europeans not only gather girls but put older women in the same houses,'' she told me. ''They get younger and older women emotionally attached. They're transported together, survive together.''

The traffickers' harvest is innocence. Before young women and girls are taken to the United States, their captors want to obliterate their sexual inexperience while preserving its appearance. For the Eastern European girls, this ''preparation'' generally happens in Ensenada, a seaside tourist town in Baja California, a region in Mexico settled by Russian immigrants, or Tijuana, where Nicole, the Russian woman I met in Los Angeles, was taken along with four other girls when she arrived in Mexico. The young women are typically kept in locked-down, gated villas in groups of 16 to 20. The girls are provided with all-American clothing -- Levi's and baseball caps. They learn to say, ''U.S. citizen.'' They are also sexually brutalized. Nicole told me that the day she arrived in Tijuana, three of her traveling companions were ''tried out'' locally. The education lasts for days and sometimes weeks.

For the Mexican girls abducted by Los Lenones, the process of breaking them in often begins on Calle Santo Tomas, a filthy narrow street in La Merced, a dangerous and raucous ghetto in Mexico City. Santo Tomas has been a place for low-end prostitution since before Spain's conquest of Mexico in the 16th century. But beginning in the early 90's, it became an important training ground for under-age girls and young women on their way into sexual bondage in the United States. When I first visited Santo Tomas, in late September, I found 150 young women walking a slow-motion parabola among 300 or 400 men. It was a balmy night, and the air was heavy with the smell of barbecue and gasoline. Two dead dogs were splayed over the curb just beyond where the girls struck casual poses in stilettos and spray-on-tight neon vinyl and satin or skimpy leopard-patterned outfits. Some of the girls looked as young as 12. Their faces betrayed no emotion. Many wore pendants of the grim reaper around their necks and made hissing sounds; this, I was told, was part of a ritual to ward off bad energy. The men, who were there to rent or just gaze, didn't speak. From the tables of a shabby cafe midblock, other men -- also Mexicans, but more neatly dressed -- sat scrutinizing the girls as at an auction. These were buyers and renters with an interest in the youngest and best looking. They nodded to the girls they wanted and then followed them past a guard in a Yankees baseball cap through a tin doorway.

Inside, the girls braced the men before a statue of St. Jude, the patron saint of lost causes, and patted them down for weapons. Then the girls genuflected to the stone-faced saint and led the men to the back, grabbing a condom and roll of toilet paper on the way. They pointed to a block of ice in a tub in lieu of a urinal. Beyond a blue hallway the air went sour, like old onions; there were 30 stalls curtained off by blue fabric, every one in use. Fifteen minutes of straightforward intercourse with the girl's clothes left on cost 50 pesos, or about $4.50. For $4.50 more, the dress was lifted. For another $4.50, the bra would be taken off. Oral sex was $4.50; ''acrobatic positions'' were $1.80 each. Despite the dozens of people and the various exertions in this room, there were only the sounds of zippers and shoes. There was no human noise at all.

Most of the girls on Santo Tomas would have sex with 20 to 30 men a day; they would do this seven days a week usually for weeks but sometimes for months before they were ''ready'' for the United States. If they refused, they would be beaten and sometimes killed. They would be told that if they tried to escape, one of their family members, who usually had no idea where they were, would be beaten or killed. Working at the brutalizing pace of 20 men per day, a girl could earn her captors as much as $2,000 a week. In the U.S., that same girl could bring in perhaps $30,000 per week.

In Europe, girls and women trafficked for the sex trade gain in value the closer they get to their destinations. According to Iana Matei, who operates Reaching Out, a Romanian rescue organization, a Romanian or Moldovan girl can be sold to her first transporter -- who she may or may not know has taken her captive -- for as little as $60, then for $500 to the next. Eventually she can be sold for $2,500 to the organization that will ultimately control and rent her for sex for tens of thousands of dollars a week. (Though the Moldovan and Romanian organizations typically smuggle girls to Western Europe and not the United States, they are, Matei says, closely allied with Russian and Ukrainian networks that do.)

Jonathan M. Winer, deputy assistant secretary of state for international law enforcement in the Clinton administration, says, ''The girls are worth a penny or a ruble in their home village, and suddenly they're worth hundreds and thousands somewhere else.''

CROSSING THE BORDER

In November, I followed by helicopter the 12-foot-high sheet-metal fence that represents the U.S.-Mexico boundary from Imperial Beach, Calif., south of San Diego, 14 miles across the gritty warrens and havoc of Tijuana into the barren hills of Tecate. The fence drops off abruptly at Colonia Nido de las Aguilas, a dry riverbed that straddles the border. Four hundred square miles of bone-dry, barren hills stretch out on the U.S. side. I hovered over the end of the fence with Lester McDaniel, a special agent with Immigration and Customs Enforcement. On the U.S. side, ''J-e-s-u-s'' was spelled out in rocks 10 feet high across a steep hillside. A 15-foot white wooden cross rose from the peak. It is here that thousands of girls and young women -- most of them Mexican and many of them straight from Calle Santo Tomas -- are taken every year, mostly between January and August, the dry season. Coyotes -- or smugglers -- subcontracted exclusively by sex traffickers sometimes trudge the girls up to the cross and let them pray, then herd them into the hills northward.

A few miles east, we picked up a deeply grooved trail at the fence and followed it for miles into the hills until it plunged into a deep isolated ravine called Cottonwood Canyon. A Ukrainian sex-trafficking ring force-marches young women through here, McDaniel told me. In high heels and seductive clothing, the young women trek 12 miles to Highway 94, where panel trucks sit waiting. McDaniel listed the perils: rattlesnakes, dehydration and hypothermia. He failed to mention the traffickers' bullets should the women try to escape.

''If a girl tries to run, she's killed and becomes just one more woman in the desert,'' says Marisa B. Ugarte, director of the Bilateral Safety Corridor Coalition, a San Diego organization that coordinates rescue efforts for trafficking victims on both sides of the border. ''But if she keeps going north, she reaches the Gates of Hell.''

One girl who was trafficked back and forth across that border repeatedly was Andrea. ''Andrea'' is just one name she was given by her traffickers and clients; she doesn't know her real name. She was born in the United States and sold or abandoned here -- at about 4 years old, she says -- by a woman who may have been her mother. (She is now in her early to mid-20's; she doesn't know for sure.) She says that she spent approximately the next 12 years as the captive of a sex-trafficking ring that operated on both sides of the Mexican border. Because of the threat of retribution from her former captors, who are believed to be still at large, an organization that rescues and counsels trafficking victims and former prostitutes arranged for me to meet Andrea in October at a secret location in the United States.

In a series of excruciating conversations, Andrea explained to me how the trafficking ring that kept her worked, moving young girls (and boys too) back and forth over the border, selling nights and weekends with them mostly to American men. She said that the ring imported -- both through abduction and outright purchase -- toddlers, children and teenagers into the U.S. from many countries.

''The border is very busy, lots of stuff moving back and forth,'' she said. ''Say you needed to get some kids. This guy would offer a woman a lot of money, and she'd take birth certificates from the U.S. -- from Puerto Rican children or darker-skinned children -- and then she would go into Mexico through Tijuana. Then she'd drive to Juarez'' -- across the Mexican border from El Paso, Tex. -- ''and then they'd go shopping. I was taken with them once. We went to this house that had a goat in the front yard and came out with a 4-year-old boy.'' She remembers the boy costing around $500 (she said that many poor parents were told that their children would go to adoption agencies and on to better lives in America). ''When we crossed the border at Juarez, all the border guards wanted to see was a birth certificate for the dark-skinned kids.''

Andrea continued: ''There would be a truck waiting for us at the Mexico border, and those trucks you don't want to ride in. Those trucks are closed. They had spots where there would be transfers, the rest stops and truck stops on the freeways in the U.S. One person would walk you into the bathroom, and then another person would take you out of the bathroom and take you to a different vehicle.''

Andrea told me she was transported to Juarez dozens of times. During one visit, when she was about 7 years old, the trafficker took her to the Radisson Casa Grande Hotel, where there was a john waiting in a room. The john was an older American man, and he read Bible passages to her before and after having sex with her. Andrea described other rooms she remembered in other hotels in Mexico: the Howard Johnson in Leon, the Crowne Plaza in Guadalajara. She remembers most of all the ceiling patterns. ''When I was taken to Mexico, I knew things were going to be different,'' she said. The ''customers'' were American businessmen. ''The men who went there had higher positions, had more to lose if they were caught doing these things on the other side of the border. I was told my purpose was to keep these men from abusing their own kids.'' Later she told me: ''The white kids you could beat but you couldn't mark. But with Mexican kids you could do whatever you wanted. They're untraceable. You lose nothing by killing them.''

Then she and the other children and teenagers in this cell were walked back across the border to El Paso by the traffickers. ''The border guards talked to you like, 'Did you have fun in Mexico?' And you answered exactly what you were told, 'Yeah, I had fun.' 'Runners' moved the harder-to-place kids, the darker or not-quite-as-well-behaved kids, kids that hadn't been broken yet.''

Another trafficking victim I met, a young woman named Montserrat, was taken to the United States from Veracruz, Mexico, six years ago, at age 13. (Montserrat is her nickname.) ''I was going to work in America,'' she told me. ''I wanted to go to school there, have an apartment and a red Mercedes Benz.'' Montserrat's trafficker, who called himself Alejandro, took her to Sonora, across the Mexican border from Douglas, Ariz., where she joined a group of a dozen other teenage girls, all with the same dream of a better life. They were from Chiapas, Guatemala, Oaxaca -- everywhere, she said.

The group was marched 12 hours through the desert, just a few of the thousands of Mexicans who bolted for America that night along the 2,000 miles of border. Cars were waiting at a fixed spot on the other side. Alejandro directed her to a Nissan and drove her and a few others to a house she said she thought was in Phoenix, the home of a white American family. ''It looked like America,'' she told me. ''I ate chicken. The family ignored me, watched TV. I thought the worst part was behind me.''

IN THE UNITED STATES: HIDING IN PLAIN SIGHT

A week after Montserrat was taken across the border, she said, she and half a dozen other girls were loaded into a windowless van. ''Alejandro dropped off girls at gas stations as we drove, wherever there were minimarkets,'' Montserrat told me. At each drop-off there was somebody waiting. Sometimes a girl would be escorted to the bathroom, never to return to the van. They drove 24 hours a day. ''As the girls were leaving, being let out the back, all of them 14 or 15 years old, I felt confident,'' Montserrat said. We were talking in Mexico City, where she has been since she escaped from her trafficker four years ago. She's now 19, and shy with her body but direct with her gaze, which is flat and unemotional. ''I didn't know the real reason they were disappearing,'' she said. ''They were going to a better life.''

Eventually, only Montserrat and one other girl remained. Outside, the air had turned frigid, and there was snow on the ground. It was night when the van stopped at a gas station. A man was waiting. Montserrat's friend hopped out the back, gleeful. ''She said goodbye, I'll see you tomorrow,'' Montserrat recalled. ''I never saw her again.''

After leaving the gas station, Alejandro drove Montserrat to an apartment. A couple of weeks later he took her to a Dollarstore. ''He bought me makeup,'' Montserrat told me. ''He chose a short dress and a halter top, both black. I asked him why the clothes. He said it was for a party the owner of the apartment was having. He bought me underwear. Then I started to worry.'' When they arrived at the apartment, Alejandro left, saying he was coming back. But another man appeared at the door. ''The man said he'd already paid and I had to do whatever he said,'' Montserrat said. ''When he said he already paid, I knew why I was there. I was crushed.''

Montserrat said that she didn't leave that apartment for the next three months, then for nine months after that, Alejandro regularly took her in and out of the apartment for appointments with various johns.

Sex trafficking is one of the few human rights violations that rely on exposure: victims have to be available, displayed, delivered and returned. Girls were shuttled in open cars between the Plainfield, N.J., stash house and other locations in northern New Jersey like Elizabeth and Union City. Suri told her mother that she was being driven in a black town car -- just one of hundreds of black town cars traversing New York City at any time -- from her stash house in Queens to places where she was forced to have sex. A Russian ring drove women between various Brooklyn apartments and strip clubs in New Jersey. Andrea named trading hubs at highway rest stops in Deming, N.M.; Kingman, Ariz.; Boulder City, Nev.; and Glendale, Calif. Glendale, Andrea said, was a fork in the road; from there, vehicles went either north to San Jose or south toward San Diego. The traffickers drugged them for travel, she said. ''When they fed you, you started falling asleep.''

In the past several months, I have visited a number of addresses where trafficked girls and young women have reportedly ended up: besides the house in Plainfield, N.J., there is a row house on 51st Avenue in the Corona section of Queens, which has been identified to Mexican federal preventive police by escaped trafficking victims. There is the apartment at Barrington Plaza in the tony Westwood section of Los Angeles, one place that some of the Komisaruk/Mezheritsky ring's trafficking victims ended up, according to Daniel Saunders, the assistant U.S. attorney who prosecuted the ring. And there's a house on Massachusetts Avenue in Vista, Calif., a San Diego suburb, which was pointed out to me by a San Diego sheriff. These places all have at least one thing in common: they are camouflaged by their normal, middle-class surroundings.

''This is not narco-traffic secrecy,'' says Sharon B. Cohn, director of anti-trafficking operations for the International Justice Mission. ''These are not people kidnapped and held for ransom, but women and children sold every single day. If they're hidden, their keepers don't make money.''

I.J.M.'s president, Gary Haugen, says: ''It's the easiest kind of crime in the world to spot. Men look for it all day, every day.''

But border agents and local policemen usually don't know trafficking when they see it. The operating assumption among American police departments is that women who sell their bodies do so by choice, and undocumented foreign women who sell their bodies are not only prostitutes (that is, voluntary sex workers) but also trespassers on U.S. soil. No Department of Justice attorney or police vice squad officer I spoke with in Los Angeles -- one of the country's busiest thoroughfares for forced sex traffic -- considers sex trafficking in the U.S. a serious problem, or a priority. A teenage girl arrested on Sunset Strip for solicitation, or a group of Russian sex workers arrested in a brothel raid in the San Fernando Valley, are automatically heaped onto a pile of workaday vice arrests.

The U.S. now offers 5,000 visas a year to trafficking victims to allow them to apply for residency. And there's faint hope among sex-trafficking experts that the Bush administration's recent proposal on Mexican immigration, if enacted, could have some positive effect on sex traffic into the U.S., by sheltering potential witnesses. ''If illegal immigrants who have information about victims have a chance at legal status in this country, they might feel secure enough to come forward,'' says John Miller of the State Department. But ambiguities still dominate on the front lines -- the borders and the streets of urban America -- where sex trafficking will always look a lot like prostitution.

''It's not a particularly complicated thing,'' says Sharon Cohn of International Justice Mission. ''Sex trafficking gets thrown into issues of intimacy and vice, but it's a major crime. It's purely profit and pleasure, and greed and lust, and it's right under homicide.''

IMPRISONMENT AND SUBMISSION

The basement, Andrea said, held as many as 16 children and teenagers of different ethnicities. She remembers that it was underneath a house in an upper-middle-class neighborhood on the West Coast. Throughout much of her captivity, this basement was where she was kept when she wasn't working. ''There was lots of scrawling on the walls,'' she said. ''The other kids drew stick figures, daisies, teddy bears. This Mexican boy would draw a house with sunshine. We each had a mat.''

Andrea paused. ''But nothing happens to you in the basement,'' she continued. ''You just had to worry about when the door opened.''

She explained: ''They would call you out of the basement, and you'd get a bath and you'd get a dress, and if your dress was yellow you were probably going to Disneyland.'' She said they used color coding to make transactions safer for the traffickers and the clients. ''At Disneyland there would be people doing drop-offs and pickups for kids. It's a big open area full of kids, and nobody pays attention to nobody. They would kind of quietly say, 'Go over to that person,' and you would just slip your hand into theirs and say, 'I was looking for you, Daddy.' Then that person would move off with one or two or three of us.''

Her account reminded me -- painfully -- of the legend of the Pied Piper of Hamelin. In the story, a piper shows up and asks for 1,000 guilders for ridding the town of a plague of rats. Playing his pipe, he lures all the rats into the River Weser, where they drown. But Hamelin's mayor refuses to pay him. The piper goes back into the streets and again starts to play his music. This time ''all the little boys and girls, with rosy cheeks and flaxen curls, and sparkling eyes and teeth like pearls'' follow him out of town and into the hills. The piper leads the children to a mountainside, where a portal opens. The children follow him in, the cave closes and Hamelin's children -- all but one, too lame to keep up -- are never seen again.

Montserrat said that she was moved around a lot and often didn't know where she was. She recalled that she was in Detroit for two months before she realized that she was in ''the city where cars are made,'' because the door to the apartment Alejandro kept her in was locked from the outside. She says she was forced to service at least two men a night, and sometimes more. She watched through the windows as neighborhood children played outside. Emotionally, she slowly dissolved. Later, Alejandro moved her to Portland, Ore., where once a week he worked her out of a strip club. In all that time she had exactly one night off; Alejandro took her to see ''Scary Movie 2.''

All the girls I spoke to said that their captors were both psychologically and physically abusive. Andrea told me that she and the other children she was held with were frequently beaten to keep them off-balance and obedient. Sometimes they were videotaped while being forced to have sex with adults or one another. Often, she said, she was asked to play roles: the therapist's patient or the obedient daughter. Her cell of sex traffickers offered three age ranges of sex partners -- toddler to age 4, 5 to 12 and teens -- as well as what she called a ''damage group.'' ''In the damage group they can hit you or do anything they wanted,'' she explained. ''Though sex always hurts when you are little, so it's always violent, everything was much more painful once you were placed in the damage group.

''They'd get you hungry then to train you'' to have oral sex, she said. ''They'd put honey on a man. For the littlest kids, you had to learn not to gag. And they would push things in you so you would open up better. We learned responses. Like if they wanted us to be sultry or sexy or scared. Most of them wanted you scared. When I got older I'd teach the younger kids how to float away so things didn't hurt.''

Kevin Bales of Free the Slaves says: ''The physical path of a person being trafficked includes stages of degradation of a person's mental state. A victim gets deprived of food, gets hungry, a little dizzy and sleep-deprived. She begins to break down; she can't think for herself. Then take away her travel documents, and you've made her stateless. Then layer on physical violence, and she begins to follow orders. Then add a foreign culture and language, and she's trapped.''

Then add one more layer: a sex-trafficking victim's belief that her family is being tracked as collateral for her body. All sex-trafficking operations, whether Mexican, Ukrainian or Thai, are vast criminal underworlds with roots and branches that reach back to the countries, towns and neighborhoods of their victims.

''There's a vast misunderstanding of what coercion is, of how little it takes to make someone a slave,'' Gary Haugen of International Justice Mission said. ''The destruction of dignity and sense of self, these girls' sense of resignation. . . . '' He didn't finish the sentence.

In Tijuana in November, I met with Mamacita, a Mexican trafficking-victim-turned-madam, who used to oversee a stash house for sex slaves in San Diego. Mamacita (who goes by a nickname) was full of regret and worry. She left San Diego three years ago, but she says that the trafficking ring, run by three violent Mexican brothers, is still in operation. ''The girls can't leave,'' Mamacita said. ''They're always being watched. They lock them into apartments. The fear is unbelievable. They can't talk to anyone. They are always hungry, pale, always shaking and cold. But they never complain. If they do, they'll be beaten or killed.''

In Vista, Calif., I followed a pickup truck driven by a San Diego sheriff's deputy named Rick Castro. We wound past a tidy suburban downtown, a supermall and the usual hometown franchises. We stopped alongside the San Luis Rey River, across the street from a Baptist church, a strawberry farm and a municipal ballfield.

A neat subdivision and cycling path ran along the opposite bank. The San Luis Rey was mostly dry, filled now with an impenetrable jungle of 15-foot-high bamboolike reeds. As Castro and I started down a well-worn path into the thicket, he told me about the time he first heard about this place, in October 2001. A local health care worker had heard rumors about Mexican immigrants using the reeds for sex and came down to offer condoms and advice. She found more than 400 men and 50 young women between 12 and 15 dressed in tight clothing and high heels. There was a separate group of a dozen girls no more than 11 or 12 wearing white communion dresses. ''The girls huddled in a circle for protection,'' Castro told me, ''and had big eyes like terrified deer.''

I followed Castro into the riverbed, and only 50 yards from the road we found a confounding warren of more than 30 roomlike caves carved into the reeds. It was a sunny morning, but the light in there was refracted, dreary and basementlike. The ground in each was a squalid nest of mud, tamped leaves, condom wrappers, clumps of toilet paper and magazines. Soiled underwear was strewn here and there, plastic garbage bags jury-rigged through the reeds in lieu of walls. One of the caves' inhabitants had hung old CD's on the tips of branches, like Christmas ornaments. It looked vaguely like a recent massacre site. It was 8 in the morning, but the girls could begin arriving any minute. Castro told me how it works: the girls are dropped off at the ballfield, then herded through a drainage sluice under the road into the riverbed. Vans shuttle the men from a 7-Eleven a mile away. The girls are forced to turn 15 tricks in five hours in the mud. The johns pay $15 and get 10 minutes. It is in nearly every respect a perfect extension of Calle Santo Tomas in Mexico City. Except that this is what some of those girls are training for.

If anything, the women I talked to said that the sex in the U.S. is even rougher than what the girls face on Calle Santo Tomas. Rosario, a woman I met in Mexico City, who had been trafficked to New York and held captive for a number of years, said: ''In America we had 'special jobs.' Oral sex, anal sex, often with many men. Sex is now more adventurous, harder.'' She said that she believed younger foreign girls were in demand in the U.S. because of an increased appetite for more aggressive, dangerous sex. Traffickers need younger and younger girls, she suggested, simply because they are more pliable. In Eastern Europe, too, the typical age of sex-trafficking victims is plummeting; according to Matei of Reaching Out, while most girls used to be in their late teens and 20's, 13-year-olds are now far from unusual.

Immigration and Customs Enforcement agents at the Cyber Crimes Center in Fairfax, Va., are finding that when it comes to sex, what was once considered abnormal is now the norm. They are tracking a clear spike in the demand for harder-core pornography on the Internet. ''We've become desensitized by the soft stuff; now we need a harder and harder hit,'' says I.C.E. Special Agent Perry Woo. Cybernetworks like KaZaA and Morpheus / through which you can download and trade images and videos -- have become the Mexican border of virtual sexual exploitation. I had heard of one Web site that supposedly offered sex slaves for purchase to individuals. The I.C.E. agents hadn't heard of it. Special Agent Don Daufenbach, I.C.E.'s manager for undercover operations, brought it up on a screen. A hush came over the room as the agents leaned forward, clearly disturbed. ''That sure looks like the real thing,'' Daufenbach said. There were streams of Web pages of thumbnail images of young women of every ethnicity in obvious distress, bound, gagged, contorted. The agents in the room pointed out probable injuries from torture. Cyberauctions for some of the women were in progress; one had exceeded $300,000. ''With new Internet technology,'' Woo said, ''pornography is becoming more pervasive. With Web cams we're seeing more live molestation of children.'' One of I.C.E.'s recent successes, Operation Hamlet, broke up a ring of adults who traded images and videos of themselves forcing sex on their own young children.

But the supply of cheap girls and young women to feed the global appetite appears to be limitless. And it's possible that the crimes committed against them in the U.S. cut deeper than elsewhere, precisely because so many of them are snared by the glittery promise of an America that turns out to be not their salvation but their place of destruction.

ENDGAME

Typically, a young trafficking victim in the U.S. lasts in the system for two to four years. After that, Bales says: ''She may be killed in the brothel. She may be dumped and deported. Probably least likely is that she will take part in the prosecution of the people that enslaved her.''

Who can expect a young woman trafficked into the U.S., trapped in a foreign culture, perhaps unable to speak English, physically and emotionally abused and perhaps drug-addicted, to ask for help from a police officer, who more likely than not will look at her as a criminal and an illegal alien? Even Andrea, who was born in the United States and spoke English, says she never thought of escaping, ''because what's out there? What's out there was scarier. We had customers who were police, so you were not going to go talk to a cop. We had this customer from Nevada who was a child psychologist, so you're not going to go talk to a social worker. So who are you going to talk to?''

And if the girls are lucky enough to escape, there's often nowhere for them to go. ''The families don't want them back,'' Sister Veronica, a nun who helps run a rescue mission for trafficked prostitutes in an old church in Mexico City, told me. ''They're shunned.''

When I first met her, Andrea told me: ''We're way too damaged to give back. A lot of these children never wanted to see their parents again after a while, because what do you tell your parents? What are you going to say? You're no good.''

Peter Landesman is a contributing writer for the magazine. He last wrote about illegal weapons trafficking.