BEIJING — 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 escape 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 herself 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 flashy 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.

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She said she would carry poison, to kill herself if captured.

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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.’”