Chen Changhua was attractive and making a good living by removing verrucas from farmers' feet. But her "boyfriend" and his friends tricked Ms Zhang all the way to Hohhot, in Inner Mongolia, thousands of kilometres to the north. Sensing something was not right, Ms Zhang demanded to be taken back, but the men claimed to have run out of money.
Chen took her to a farmer's family in a desert village, supposedly to borrow money. "When Chen readied himself to go, I got up, too. But the family pushed me down. I didn't understand what they were saying. Then the hard truth hit me: I was sold for 3600 yuan [$520]!" she recalled.
Every year, thousands of Chinese women are kidnapped and sold to farmers as their wives. The Government has staged numerous campaigns against human trafficking, featuring highly publicised arrests and heavy sentences for the kidnappers. But despite wave after wave of these campaigns, the practice still thrives in the countryside, causing untold misery and pain for the victims and their families.
"The 32 months were hell," Ms Zhang said, wiping tears as she sat in her small flat in Zhongjiang. On the first night, Bai Jinquan, her buyer, climbed into her bed.
"He was so dirty, smelly and old - I never knew how old he was, too old for me anyway. I was scared to death," she said.
She fought him off, but Ms Zhang soon realised she was a prisoner. She was followed everywhere. On the second night she tried to escape but was soon caught. Bai dragged her back by her feet, beat her unconscious, then raped her.
"I dreaded night-time when Bai came up to me, his dirty hands pulling off my trousers," she said, eyes looking down at her tea. She gave up resisting his daily demands only after Bai threatened to sell her off: she had heard stories of bought wives being shared by several brothers.
Homesick and desperate, Ms Zhang wrote many letters, but none was sent except one asking her mother to come and help after she became pregnant.
But help did eventually come in the form of an unlikely hero - Zhu Wenguang, a 44-year old security guard turned private detective. Short, with a pot belly, Mr Zhu, who is known locally as Zorro, has rescued more than 160 women, including Ms Zhang.
At her mother's request, he arrived in a van with three local policemen to set Ms Zhang free.
Angry villagers mobbed the van, shouting: "Don't let the woman go!" and Bai hit Mr Zhu with an iron rod. Mr Zhu persuaded Bai to get into the vehicle, on the pretence of solving the dispute at the local government offices. In fact Bai and his brother were taken to the police station where they were arrested for hitting a policeman, but were later discharged.
Ms Zhang got away and spent her first night as a free woman at a hotel next to the police station. "I began to miss my son. He was only six months but Bai's family wouldn't allow me to take him."
Leaving their babies behind is the greatest dilemma and personal torment faced by women in Ms Zhang's situation.
Mr Zhu said more than 90 per cent of the women he rescued were happy to leave. Those who chose to stay with their captors did so because they could not leave their children.
An Asia-Pacific conference on Reproductive and Sexual Health and Rights was warned this week that a rising gender imbalance in Asia would lead to an increase in sex trafficking and social instability if not addressed. There are 2.1 billion men in Asia, against 1.9 billion women.
The French demographer Christophe Guilmoto said the problem was particularly acute in China, where studies had shown men would outnumber women by 25 million in the year 2050.
After the founding of the people's republic in 1949, the age-old customs of wife-buying and forced marriage were banned. But during the past two decades of economic reform, millions of rural residents have migrated to urban centres in search of better-paid jobs. Women have found work in the cities as maids and in factories, or have married into richer villages. The men left behind have fewer choices.
Sons are expected to stay on the family farm and look after ageing parents. Some farmers prefer to buy a wife because it is much cheaper than the requisite dowry and wedding banquet, which can cost up to 10,000 yuan.
The All-China Women's Federation has repeatedly lobbied the Government to eradicate the illegal trade in women, which also brings back other feudal practices, such as child marriage and polygamy.
The official Xinhua news agency reported that between 2001 and 2003 police rescued 42,215 kidnapped women and children. The true tally is believed to be much higher. Revised laws have imposed harsher punishment on human traffickers. But for many, the Government's action to solve the problem is falling far short of what is needed.
Mr Zhu started his journey as Zorro in 1994 when he was working as a gatekeeper for the Zhongjiang police station.
Bride kidnapping was rampant then. "I met so many people who came to the [police station] seeking police help. But most cases were simply not dealt with. I was most sympathetic because the same tragedy happened to my auntie's family," he said.
After repeated requests, he was sent on a trial mission to Inner Mongolia to rescue a 21-year-old woman, Deng Xiaoying, and her 15-year-old niece. He won over the local policemen by treating them with a banquet and claimed the women were his relatives. Together, they raided the buyer's home at night, pretending to check their residency documentation.
The freed women knelt down in front of Mr Zhu and called him their "saviour". "I was totally moved and I became addicted," he admitted.
Mr Zhu's chivalrous act won him the Zorro reputation and plenty of media attention, but also brought trouble. One senior official said: "You made us police look useless."
Due to pressure from authorities and changed personal circumstances, Zorro is planning to give up his rescue missions. In a rare public acknowledgement of the kidnapping problem, Bai Jingfu, deputy general director of the Ministry of Public Security, recently pointed his finger at weak social control and the huge profits involved as the main causes.
It was money that drove Tan Haiping, 44, to become a professional human trafficker. In early 1990, he tricked his first victim, a 15-year-old girl from his neighbourhood in Zhongjiang, to travel to Henan province to see his friend, "Uncle" Jiang, who had hoped that Tan would introduce him to a girl for his son to marry.
"When Jiang gave me 2000 yuan, I thought, hey, this was a quick and easy way to make money," Tan said. Back at home he would chat up girls at the local cinema who were sitting by themselves. If they responded, he then took them for dinner, always showing off the wads of money in his wallet. He told the girls that he had a great job at a factory in Henan, and he could get them a job there, too.
"It was quite easy. They all wanted to go out to work as migrants," Tan boasted. With a bit of luck, he would take the girls to bed and then drag them to Uncle Jiang once he had had enough of them. Uncle Jiang had also become a member of the human trafficking chain.
Other traffickers lurk around black job markets or train stations, preying on naive women, often using job offers as bait. Women are often kidnapped from Sichuan, Yunnan and Guizhou, and sold to farmers in Inner Mongolia, Shanxi, Shaanxi and Henan. Some dealers rape their victims first, while others play the virgin card for higher bids.
Tan's champagne lifestyle did not last. With Mr Zhu's assistance, the first victim's mother managed to get him jailed for three years. "I swore that I would kill Zhu. But now I am grateful to him. If I had not gone to jail, I would most likely be dead now: traffickers get death sentence instead of getting away with a few years behind bars," Tan said.
China's family planning policy, which restricts most families to one child, has led to serious imbalances in the sex ratio, due to sex-selected abortions and infanticide.
Rural families often want boys to carry on their family line. The Family Planning Association predicts that by 2020 37 million Chinese men will not be able to find a woman to marry.
"The unbalanced ratio makes it harder to wipe out this evil practice. But kidnapping women is a difficult subject for the mainland academics to research," said Peng Dinding, an economist who conducted research for Martin Adler's award-wining TV documentary Abduction. "Also, like other crackdowns, once the campaign is over, the Government pretends the problem no longer exists. It still does, and in some remote parts, seriously."
Mr Zhu still gets plenty of pleas from distraught families. In September 2005 he rescued Dai Xiaozheng from a village in Shanxi province. One year earlier, Ms Dai, only 15, had been plucked from Zhongjiang by a man who promised her a job. She was sold to a young farmer, Ma Liang. When the teenager, shocked and traumatised, refused to be his wife, the farmer took her to a karaoke bar owned by a friend in Datong city and forced her to sing and sleep with clients. Using one of his clients' mobile phone, Ms Dai finally called her family, who then turned to the detective for help. "The little thug had total control over her because she had no money or ID, and didn't speak the local dialect," Mr Zhu said.
Compared with the many thousands of women who remain trapped in involuntary marriages, a long way away from home, Ms Dai and Ms Zhang are some of the lucky ones. But the shadow of the past still haunts them. "I hate myself for being stupid and I hate those heartless people who sold me. They ruined my life," Ms Zhang said.
To fund her rescue, Ms Zhang's family borrowed a substantial sum from a man who was keen to find a wife to marry. To cancel the debts, and feeling grateful to the man, Ms Zhang married him. "Deep down, he always regarded me as a 'stained goods'," she said. The marriage did not last. Ms Zhang admits that, because of her horrifying experiences, she is not interested in the "bedroom business". "I don't want to talk about the past. It hurts my heart just to think about it," she said, clutching her teacup.