BEIJING (NYTIMES) - Ms Choi was worried about her sister in North Korea.
The last time they spoke, two months earlier, her sister had sounded desperate. She said she had been imprisoned and beaten, and could no longer bear the torment. She said she wanted to flee and join Ms Choi in South Korea.
She said she would carry poison, to kill herself if she were captured.
For Ms Choi, 63, a grandmother with large brown eyes and a steely fortitude, getting the rest of her family to South Korea was the most important thing left in life. She had fled North Korea 10 years ago. Her son had made it out too, as had her sister's daughter, now a hairdresser living near her in Seoul, the South's capital.
Ms Choi longed to be reunited with the sister, a 50-year-old dressmaker with her own home business, and also the nephew she had left behind.
She wanted to get them to safety, out of the reach of the government that had arrested her husband, her brother-in-law and her son-in-law on suspicions of helping people leave. They had been targeted as enemies of the state and were never seen again.
One evening this past summer, Ms Choi got the news she had been waiting for.
As she opened her apartment door, her niece, 25, shouted: "My brother called. He said: 'We crossed the border. We're in China. Get the car.'"
Ms Choi, who must go by only her last name to protect her and her family against possible retribution from the North Korean government, was jubilant. But she and her niece felt a new anxiety.
Defectors usually leave North Korea by crossing into China. The border is tightly guarded by soldiers under the command of the North Korean leader, Mr Kim Jong Un, who views those trying to leave as traitors.
Once in China, defectors must rely on smugglers who charge extortionate rates to evade Chinese security and North Korean agents. Capture or betrayal could lead to prison, or worse.
They often make their way to China's southern border to seek passage to a third country, usually Thailand. From there, the South Korean government flies defectors to Seoul.
The attitude of the Chinese government makes the journey even more dangerous. Although China's relations with North Korea have soured, China pleases North Korea by detaining any defectors it finds and returning them to almost certain harsh imprisonment, and possible torture.
China has forcibly deported tens of thousands of North Koreans - a conservative estimate since there are no statistics available - and looks the other way when North Korean agents capture defectors inside its borders, according to the Committee for Human Rights in North Korea.
In total, around 30,000 North Koreans have made it to the South, where they are welcomed with free housing, inexpensive medical care and training for the cutthroat job market.
However, the passage has become more difficult since Mr Kim became the North's supreme leader in 2011. Last year, 1,127 North Koreans arrived in the South, just one-third of the annual number before he came to power.
China deports the North Koreans despite having signed a 1951 United Nations convention not to return refugees to countries where they will suffer persecution.
The United States, the European Union, South Korea and the UN regularly ask China to stop such repatriations of defectors, whom they consider political refugees.
China has paid no heed. It says it views the North Koreans not as political refugees but as economic migrants seeking jobs.
It says it sends them back because it cannot afford to have its depressed northeastern region destabilised by an influx of outsiders.
Ms Choi and her niece faced an early hitch. The group of defectors was larger than they had expected. The sister and her son, 28, were joined by the son's girlfriend and two of his friends.
Now there were five people to move through China without attracting notice.
Ms Choi and her niece phoned a South Korean man whom they had hired to handle the escape. Known in the smuggling business as a broker, he had arranged the niece's journey out of the North during less tense times five years earlier.
The group of five could hardly have picked a more precarious time to flee into China.
Chinese security was on high alert, searching for North Korean defectors. China was angry at South Korea for deploying a US missile defence system, known as a Terminal High Altitude Area Defence (Thaad).
The Chinese saw rounding up North Korean defectors who were heading to South Korea as a way to irritate the government of the South's newly elected President, Mr Moon Jae In.
At the same time, China's leader, Mr Xi Jinping, was pressing an anti-corruption campaign that was making Chinese officials much less amenable to the bribes often offered by brokers to release North Koreans arrested at the border.
Making it to South Korea depended on the skill and reliability of the broker.
Ms Choi and her niece had paid the broker an advance fee of US$13,000 (S$17,070.30), most of it earned by the sale of the niece's apartment in Seoul.
The broker hired by Ms Choi and her niece was rusty at the job, and greedy. Instead of handling the sister's journey himself, he sub-contracted the case to a North Korean woman in Seoul who was married to a Chinese man. The husband, in turn, hired a relative in China to pick up the group in a van after they sneaked across the border.
The relative was then supposed to drive them to Shenyang, a city in northeastern China that is often used by North Korean defectors as a base before heading south.
The Yalu River separates China and North Korea. The river is low in the summer. The sister's group waded across.
Once across, they got lost in the woods. For two days, they wandered along the wild eastern edge of China in hills above the town of Changbai, looking for the driver.
Finally, the North Koreans found their way out of the woods. The driver located them at 2am on the edge of Changbai.
Her nephew phoned. "We're saved. We're going to live," he said.
The last word came from the group came at 10am, when they were approaching their destination.
Then there was silence.
At first, the broker in Seoul and his subcontractor, the North Korean woman, could not explain what had happened. "We are looking for them," the woman told Ms Choi.
Soon, the woman provided an explanation: The five had been taken hostage.
Several days later, she changed her story: "They must have been arrested."
More money would be needed for their release.
Carrying a wad of cash, the sub-contractor jumped on a plane to Changbai, where she thought the group was being held.
The North Korean woman who went searching for the group in China returned empty-handed.
Word seeped out from North Korea that photographs of the five had appeared on a municipal notice board in their hometown - a sign that they were dead.
Rumours circulated in the defector community that five bodies had been returned to North Korea. But there was no concrete evidence, no photographs of the bodies.
The Foreign Ministry in Seoul said it had asked China about the fate of Ms Choi's sister and her four companions. In this case, China did not reply.
Asked about the case, China's Foreign Ministry in Beijing repeated its standard line: that China treated fleeing North Koreans as illegal migrants who were dealt with according to international and domestic laws, and sometimes humanitarian considerations.
A senior ministry official refused to accept copies of the photographs of the missing five, or to inquire about them at the Chinese detention centres along the border.
Human Rights Watch said that what little information it had suggested that the five had killed themselves. But there was no definitive proof, a spokesman said.
What does Ms Choi think happened?
"My niece and I believe my sister and her son took their lives," she said. "But it's not clear whether all five killed themselves."