Gao Zhisheng, one of China’s most irrepressible dissidents, began the day of Jan. 9 the same way as most days since security officials had begun watching him around the clock. He and his wife, Geng He, ate a breakfast of soy milk, fried eggs and peanuts. Mr. Gao left the apartment to run some errands.

By the time he returned, his wife and two children were gone. With only the clothes they were wearing, roughly $60 in cash and, out of habit, their keys, the three embarked upon a harrowing odyssey orchestrated by human rights activists that began in the bitter cold of northern Beijing and ended, seven days and some 2,000 miles later, in the humid safety of Thailand.

“I had no time to think,” Ms. Geng, whose children are 16 and 5, said. “I didn’t have a watch. I had no concept of time. All I knew was that we had to move forward. We couldn’t go back.” She spoke during an interview late last month in New York, where she and her children settled after arriving in the United States in March.

Ms. Geng’s tale stands out not just because it involves a cinematic escape, with elements like stalled motorcycles and nonstop travel with little food or sleep. It is remarkable, human rights activists say, because it reveals how China uses family members of dissidents as leverage against them. And it shows the extreme measures a small number of political opponents will take to deny the authorities that leverage. Ms. Geng insists, though, that her husband knew nothing of her plans.

Mr. Gao said in earlier interviews that security officials used threats against his children to extract a humiliating public confession from him in 2006. So the departure of his family gave him greater leeway to challenge the leadership, though at a high cost: he has not been seen or heard from since Feb. 4, when the security forces hauled him away.

His family’s escape upended the way security officials managed the provocative Mr. Gao, a human rights lawyer who has embraced causes including the outlawed spiritual group Falun Gong, displaced urban residents and the Christian underground church. He issued angry manifestos calling for the end of Communist Party rule.

Since his release from prison in 2006, Mr. Gao had been allowed to live a superficially normal life in Beijing. But he was shadowed by plainclothes guards, and he said he felt constrained by the threat of retribution against his family if he violated the terms of his parole.

Though he has not been charged with a new crime, he has vanished altogether since three months ago.

Mr. Gao’s disappearance has become a delicate diplomatic issue ahead of the 20th anniversary of the Tiananmen Square democracy movement on June 4. Laura Tischler, a State Department spokeswoman, said that American diplomats had not yet met with Ms. Geng. But she said that a senior American official discussed the case on March 31 with high-ranking Chinese officials in Beijing, and that State Department officials had raised the case, most recently on April 15, with the Chinese Embassy in Washington.

“The United States is deeply concerned about the safety and well-being of well-known human rights lawyer Gao Zhisheng,” Ms. Tischler said. “We have raised our concerns about Mr. Gao’s whereabouts and well-being repeatedly, both in Washington and in Beijing.”

Congress is watching, too. With Ms. Geng in the gallery, Senator Byron L. Dorgan, a North Dakota Democrat, saluted her courage during a Senate floor speech on April 23 and warned that Mr. Gao, a “devout Christian,” had been thrust into an “extremely grave” situation.

“There are many today that languish in dark cells, dark cells of Chinese prisons, just because they spoke out to defend the rights of others,” said Mr. Dorgan, who is the chairman of a Congressional commission responsible for monitoring China’s human rights record. “None have done so more than Mr. Gao.”

Beijing officials, however, say that nothing untoward has happened to the Gaos.

“There’s no political persecution or limits on the freedom of the family,” Qin Gang, a spokesman for the Foreign Ministry, said at a briefing in Beijing in March. “We’ve handled the case in strict accordance with the law.” In response to inquiries about Mr. Gao’s whereabouts, the Chinese authorities have not furnished further information and have not acknowledged that he was taken into custody.

Mr. Gao, 45, was once a populist litigator battling corruption and land seizures, and he was recognized by the Ministry of Justice in 2001 as one of China’s 10 best lawyers. But he became more active handling cases of police abuse and religious freedom for Christian churches and the Falun Gong. In 2006, he rallied grass-roots organizers around China to go on a hunger strike to protest the way security forces treated another activist. He was later arrested and convicted of sedition. In December 2006, he was given a suspended sentence because, the authorities said, he confessed to his crimes and provided information about other dissidents.

The next year, Mr. Gao said his confession had been coerced. Interrogators threatened to punish his children and deny them an education unless he cooperated, he said in April 2007. “In the end I decided I could not haggle about my children’s future,” he said. He was tortured, Ms. Geng and human rights watchdogs say, with electric prods, bamboo sticks lancing his genitals, and cigarette burns to his eyelids.

Mr. Gao continues to suffer from ailments that Ms. Geng attributed to his “zhemo,” or torment, a word she used repeatedly during the interview, which was conducted in Mandarin at the offices of Human Rights in China, a watchdog group. “My husband may be in his 40s, but he’s got the body of someone in his 60s,” she said.

For Ms. Geng, the turning point came last September, when her daughter, Geng Gege, now 16, stopped going to school. The teenager felt ostracized by her peers; they felt that her father’s status was the reason everyone’s cellphone had been confiscated, and why the police shadowed her to and from class.

“Her classmates would bully her and say, ‘Your father is involved in organized crime,’ ” Ms. Geng recalled, her voice trembling. “She could not handle it anymore and she tried to kill herself.”

Because of her daughter and her 5-year-old son, Gao Tianyu, Ms. Geng decided to flee. And on Jan. 9, when she got the signal from activists that it was time, she hurriedly scribbled a brief note for her husband and left it on the dining table. It read, “I am taking Gege to school,” she said.

“I did not tell my husband because I didn’t think he could take it,” she said.

The journey was fraught with danger and paranoid moments. The family was always moving, usually at night, via overnight trains, overnight tour buses and motorcycles, and on foot. Only once did they stop overnight at someone’s house.

The most trying moment, Ms. Geng said, came when, for security reasons, the guides separated her from her son for several hours. Their motorcycles could not make it up a slippery hill, Ms. Geng said, and she got into an argument with her daughter.

“She said, ‘I’ll go to jail, I don’t care! I can’t do this anymore,’ ” Ms. Geng recalled, continuing, “I begged her not to give up, because we had to be reunited with Tianyu. I was worried that I would be separated from my child forever.”

Ultimately, the three made it to Thailand, where they were granted refugee status, facilitated by international rights groups including China Aid, a Christian organization based in Midland, Tex., which has sought to promote Christianity and protect underground church leaders in China.

Ms. Geng says she is still adjusting to her new life, settling in an apartment in Fresh Meadows, Queens, with the assistance of the American government. Her children are taking English classes but are worried about when they will see their father again.

One night last month, Ms. Geng woke at 3 a.m.; the light was still on. Her daughter was staring at a computer, donated by a friend. The screensaver image was Mr. Gao.

“She said, ‘I just want to say a few things to my dad,’ ” Ms. Geng recalled, sobbing. “ ‘Go back to sleep, Mom.’ ”