The infrared camera showed them clearly, a man and a woman whose skinny legs barely managed the rough flow of the river. The man pulled at the woman's hand. Already the water was waist high. The woman paused, looking dizzy. The man swiftly looked around. He pulled her along. It took them more than 10 minutes to cross less than 4 yards.

The man was a human trafficker and she was his client. They were shivering, rushing to put on the clothes they carried in a plastic bag. The man was to go back to North Korea shortly, and wet clothes would arouse suspicion, and she did not have anything else to wear. That was why they crossed the freezing water in their underclothes.

The woman, Mun Yun-hee, was 25 years old. "A 25-year-old costs at least 5,000 yuan," the man said. When we tried to negotiate, he got angry. "It's 7,000 yuan for up to 24 years old, and 3,000 yuan for over 30. That's it. Look somewhere else for a discount."

Mun Yoon-hee gets dressed after crossing the Duman or Tumen River in her underwear.

While Yun-hee was putting on her clothes and shoes, a staffer from Durihana Mission, a South Korean charity for North Korean refugees, paid the trafficker. The mission helps North Korean women escape, preventing them from being sold to Chinese men. The trafficker counted the money. Yun-hee was freed from famine only to become a sex and housekeeping slave for the rest of her life, for a price of a mere 5,000 yuan, or around W680,000. That is 30 times the salary ordinary North Koreans earn, but only W46,000 of the money would go to pay off some of her family's debt, and the rest to the trafficker.

The next day, we met Yun-hee at her shelter. She had escaped and been forcibly repatriated once before. "I myself went to the man to ask him to sell me. Our family owed almost 700 pounds of grain with no means to pay it back," she said. "The broker promised to pay back half of our debt. He is one of our neighbors, as wealthy as a Chinese with his own farm, with couches, a TV, and a fridge. The Army and the State Safety and Security Agency all know he sells women." But no one touched him. Why? "Because he has money. Why would he get punished with lots of money?" she added.

In January this year, we found a North Korean woman who had frozen to death in the Duman or Tumen River in China. Shoeless, her feet wrapped only in cloth, she lay dead on her stomach in the middle of the frozen river. For over two months until March 2, she had lain there as no one claimed her body.

That morning, Yun-hee went out with the broker. After lunch, they hid in the hills, and at dawn there was a light signal from the North Korean Army below. They took their clothes off and went over the river to step on Chinese territory for the second time.

The first time, she was sold to a 34-year-old Chinese man in Shandong Province in 2006. Six months later, public security officers arrested her. Asked how they found her, they said a neighbor had informed on her. She was immediately sent to Dandong prison and from there deported to Shinuiju with a group of North Korean detainees, chained together in pairs.

There, she was thrown into a security detention center for a month. They checker her blood for venereal disease and did a cavity search. Male inmates are forced to bang their heads against the steel door and are beaten with clubs when they resist. Pregnant inmates are forced to miscarry on the grounds they are bearing "impure" Chinese children. "The meals were so poor that we longed for the food we were given in the Chinese prison," she said. Transferred to an escapee camp in Chongjin, North Hamgyong Province, she was released after a stint of hard labor in 17-hour shifts. Several months later she again entrusted her body to a trafficker.

An official from the Durihana Mission asked her if she wanted to go to South Korea. She did not hesitate to say, "I'll go back to the Chinese man who bought me first. I want to live with him, eat plenty and earn money to send to my family." For the benefit of her blind old mother and younger brother, she opted to stay in China, risking another deportation. The Durihana Mission official failed to persuade her and said goodbye after buying her a few pieces of winter clothes.

The body of a North Korean woman has been left unattended for more than two months.

"It is the first time in the 10 years since the famine in North Korea that we saw a body," said one Korean Chinese. "Judging from the way she looks, she must have died tripping on a stone while she tried to escape by herself."

The porous North Korean-Chinese border is a hotspot for human trafficking, with many North Korean women sold into indentured servitude in China.