HUONG was only 15 when she went out to meet a friend in Lao Cai, a city in northern Vietnam on the Chinese border (see map). She thought she would be gone a few hours, but it was three years before she managed to return home. Her friend had brought with her two acquaintances—young men with motorcycles. They squired the girls around town and took them to a karaoke bar, where their drinks were spiked.

When the girls grew drowsy they were hoisted back onto the bikes, each sandwiched between two male riders. They were driven into the hills and across the Chinese border to a remote house in the countryside. There they were told they would be sold. The girls screamed and cried but were subdued by two men, one of them wielding a stick. The traffickers told Huong that by crossing the border she had sullied her reputation, but that if she behaved well they would find her a Chinese husband. After marrying she might find a way home, they said. If she refused she would stay stranded in the hills.

Huong—a pseudonym, to protect her identity—is now 20 years old. She lives in a large bungalow in Lao Cai, which she shares with a dozen women aged between 15 and 24 (an occupant is pictured). They are all survivors of trafficking networks that smuggle girls across the Vietnam-China border, sometimes to be sold as prostitutes but more often as brides. Their house, with its enormous teddy bears and fleet of fuchsia-pink bicycles, is a shelter run by Pacific Links Foundation, an American charity, which helps victims finish their education and cope with their trauma.

Around the world some 15m people are living in marriages into which they were forced, including some who were abducted, according to a recent study by the International Labour Organisation, a UN body, and human-rights groups. In China the trafficking of women is particularly acute, in part because a preference for sons has left the country with a severely skewed sex ratio. Between 1979 and 2015 the imbalance was aggravated by a one-child-per-couple policy, which prompted many to abort females before they were born. The Chinese Academy of Social Sciences has estimated that by 2020 there will be 30m-40m Chinese men who will be unable to find wives in their own country.

One consequence of this is booming business for matchmakers who offer to import women from China’s poorer neighbours, particularly Laos, Myanmar, Cambodia, Vietnam, Mongolia and North Korea. Some of these women, seeking a route out of poverty at home, freely choose a Chinese marriage and gain the necessary approvals. But along China’s borders, kidnapping is rife.

The stories told by trafficking survivors and Vietnamese officials in Lao Cai shed light on this grim trade. Each year between 100 and 150 trafficked Vietnamese women return to their country through the town’s border gate, says an official there—probably only a small proportion of the total who are lured or abducted the other way. Some of the victims’ ordeals begin when, like Huong, they are drugged or kidnapped. Others are duped into thinking they are going to a party or to meet a potential boyfriend. Sometimes members of their own families are complicit.

Groomed online

Diep Vuong of Pacific Links thinks victims are getting younger (in China, women have to be at least 20 to get married, but marriages to abducted foreigners are often unregistered). The spread of cheap smartphones and improvements in mobile networks are making it easier for traffickers to use social media to befriend schoolgirls in Vietnam’s hills. These criminals earn as little as $50 for each woman they bring into China, where they are often resold far inland by middlemen. Chinese police report that at their final destination Vietnamese women fetch prices of between around 60,000 and 100,000 yuan ($9,000-15,000).

Some snatched women and girls return home swiftly. A 17-year-old who lives at the bungalow with Huong says she was gone for only two days before a woman on the Chinese side of the border helped her to escape. A fellow resident, who returned from China a month ago, walks with a limp. She says she broke her leg leaping from the house in which her traffickers were holding her. Chinese police later found her lying in the street.

Huong’s story is longer. She was kept at her traffickers’ house and threatened for two months. When she finally agreed to be married she was driven for two days to a city in Anhui, a province north-west of Shanghai. She was warned not to let her new family find out that she was Vietnamese. She was to pretend to be a Chinese citizen belonging to an ethnic minority with cross-border cultural links.

The man to whom she was sold into marriage was in his early 20s. He was from a wealthy family, which had paid 90,000 yuan for her. Her husband explained that he had not really wanted to get married, but that his parents were keen. They had told him that an ethnic-minority bride would be more obedient than someone from the ethnic-Han majority. Such claims are commonly made by matchmakers. One Chinese mail-order marriage site says Vietnamese women are cheap, obedient and unlikely to run away: they are “so gentle and loving they will make you melt”.

The greatest demand for foreign wives is in the countryside, particularly among men who are poor or disabled, says Jiang Quanbao of Xi’an Jiaotong University. In rural areas not only is the sex ratio an impediment to finding a bride, so too is the migration of women to the cities in search of work and higher-status males. Impoverished villages sometimes end up with dozens of foreign wives, as word spreads of their availability.

Villagers often have sympathy for the buyers—they may even help to prevent trafficked women from fleeing. Escape is not at all simple for women without money of their own and with limited Chinese-language skills. North Koreans who contact the authorities risk being repatriated and then sent to concentration camps. That makes them particularly vulnerable to traffickers. Amid rising tensions on the Korean peninsula caused by North Korea’s nuclear tests, police in nearby Chinese provinces are becoming more watchful for unauthorised migrants from across the border, including North Korean women who have been sold into marriage.

Once victims become mothers, their decisions about whether and how to leave China become even more difficult. So it was for Huong. She had been taken to Anhui with another Vietnamese girl who was being sold into the same district. The pair agreed that they would find a way home together. But their plan had to be postponed soon after arrival, because Huong’s friend became pregnant. By the time the baby was delivered Huong was expecting a child, too. Less than a month after she gave birth, Huong’s in-laws sent her to live and work at a textile factory nearly four hours away, leaving her baby behind. Her husband would turn up on payday to collect most of her wages—about 6,000 yuan a month. Eventually Huong concluded that the family meant to keep her estranged from her daughter. She resolved to escape back to Vietnam.

Huong scraped together enough money to travel independently. Her own parents, whom she had managed to contact a few months after reaching Anhui, helped her work out where best to present herself to the authorities. The Chinese police kept her for three months while they investigated her story, after which they arrested some of the people involved in trafficking her. Then they sent her back to Vietnam, though her baby remained in China.

In June the American government reported that China was “not making significant efforts” to tackle human trafficking. It relegated China to the ranks of countries, such as Venezuela, Turkmenistan and South Sudan, which it rates as the worst for their record in dealing with the problem. But Chinese police say they are not sitting on their hands. They report that between 2009 and the middle of last year, they “rescued several thousand women of foreign nationality” in anti-trafficking operations that involved co-operation with their counterparts in Vietnam, Myanmar and Laos (pictured are victims being sent back to Vietnam by Chinese police in 2015). More than 1,000 people were arrested for related crimes.

In some provinces government registrars are trying to spot unwilling foreign brides by hiring staff with knowledge of regional languages. The government says that stricter policing last year in the borderlands reduced trafficking from Vietnam.

It is difficult, however, to prosecute people for buying abducted women. In 2015 the law was revised to make legal action easier. But the law says that, in cases where the woman wants to return and the buyer does not try to prevent it, punishment can be lighter or the sentence can be commuted. Cross-border operations remain hostage to China’s relations with its neighbours. Ties with Vietnam, an age-old rival, are often frosty.

Huong is now finishing high school, and hopes to study medicine. She says she “will not regret” having to leave her daughter in China. A baby would have been a burden on her family in Vietnam, and she worried that having no father would thrust the child into a legal limbo. Her in-laws were wealthy, at least, and seemed devoted to her daughter, she says. They were “good people.”