Afterward, I'd given Wen my card, telling him, a bit apprehensively, that I was pretty tough on his government. "Please continue," he'd said. I had often remembered that encounter but never expected to see him again. It was a surprise to find he would be my guide for the second leg of a trip friends had helped arrange so that I could meet Chinese dissidents in Beijing and Hangzhou.

The week before I arrived, some 40 intellectuals, journalists, lawyers, and human rights activists had released a letter decrying the condition of human rights, particularly at a time when Chinese leaders were using the 2008 Summer Olympic Games, to be held in Beijing, to enhance China's international prestige. Over the ten days I was in China, I met several dissidents who had signed the open letter.

Hangzhou is a tourist city with a large lake and historic villas where Mao Zedong, Chiang Kai-shek, and literary figures used to vacation. Wen, who is in his mid-30s, spent several years working in the import-export business before turning more or less full time to writing and civic action. Fifteen minutes into our ride, he told me that two black cars had been with us since the airport. They followed us for the next three days.

I hadn't noticed any surveillance in Beijing, and neither had my guide there--a scientist whose career had been derailed by his involvement in the protests at Tiananmen Square, violently suppressed by the government on June 4, 1989. Yet I'd visited one of China's most prominent dissidents, Ding Zilin, the mother of a teenager killed in the Tiananmen massacre. Possibly someone watching her apartment, or that of another dissident I visited, the literary critic Liu Xiaobo, had seen me and alerted the authorities in Hangzhou. Before my trip, my friends and I had agreed that it was actually a good thing for the authorities to know the dissidents had supporters outside China. Now, seeing the black cars in the side-view mirror, I still believed that, but I couldn't help worrying.

Wen had planned to register my hotel room in his name so I wouldn't have to turn over my passport to the hotel, which reports information to security officials. We went through with this plan even though it didn't make sense any more. Over the next few days I met with a human rights lawyer, a journalist who had been fired for reporting on the demolition of an unauthorized church building, and a writer who publishes articles with titles like "Hu Jintao: Kneel Down Before Me" on overseas Chinese websites.

The dissidents in China walk a tightrope. The Communist party allows certain things, but draws the line at others. The dissidents I am writing about here communicate fairly easily with each other and with the outside world. When they are careful, there is a kind of modus vivendi with the authorities. But there are some things they know they cannot do without serious consequences.

The case of my guide in Beijing, the scientist Jiang Qisheng, is a good example. The party refuses to reverse the official position that the demonstrations of 1989, joined by protesters in cities throughout China, were the work of a "small handful" of counterrevolutionaries. To commemorate Tiananmen as a tragedy and question the official position is to challenge the party's legitimacy. In 1999, Jiang wrote an open letter encouraging Chinese people to remember and honor the victims of Tiananmen. Then he talked about it on Radio Free Asia, the U.S.-funded service that broadcasts into China in Mandarin. He was promptly arrested and sent to jail for four years. "What I did, what landed me in prison, was really quite simple," he wrote in the New York Review of Books after he was released in 2003. "I just said in public what my fellow citizens were saying" in those "nooks in China where ordinary people have determined that they can speak their minds without incurring disaster." The party cannot tolerate any call to the Chinese people on an issue as sensitive as Tiananmen; speaking directly to the nation on Radio Free Asia--as opposed to writing for a mainly American audience--crossed a line.

One problem is knowing where the line is. Another is deciding whether you are willing to cross it.

On its face, the August letter is quite bold. It condemned human rights abuses and showed the signers have no illusions that merely hosting the games will moderate the behavior of China's Communist party rulers. "We, as citizens of the People's Republic of China, ought to be feeling pride in our country's glory in hosting the Games, whose purposes include the symbolization of peace, friendship, and fairness in the world community.  .  .  .  Instead we feel disappointment and doubt as we witness the continuing systematic denial of the human rights of our fellow citizens even while--and sometimes because--Olympic preparations are moving forward."

Yet the letter--reported around the world and relayed back into China via Chinese language websites monitored by the regime--stopped short of calling for a boycott of the Olympic games, which the signers thought would trigger a harsh reaction from the government. The letter also asked for the creation of an independent group to monitor preparations for the Olympics. The dissidents know, however, that if they actually set up such an independent group, it would be crushed.

The letter also did not mention the Tiananmen massacre, despite the pall it still casts over China. In the days after the letter's release, I was able to visit Ding and her husband, both retired professors in their early 70s. After their 17-year-old son was killed, Ding began gathering information about what happened the night of the Tiananmen massacre. She started by collecting the names of the victims. Despite official harassment, she interviewed relatives of the victims to document their deaths and counter the official denial; one man told her that, looking for his brother at a hospital morgue, he was shown just a hand. Ding and another mother began speaking to foreign reporters about their children. Other relatives joined their efforts. They became the Tiananmen Mothers, a group of nearly 200. Now they themselves are getting old and beginning to die.

Several years ago, security officials came to Ding and told her they wouldn't post agents at her building if she promised not to meet with foreigners and journalists at home. She refused. It was their job to keep people away, she said. If visitors made it to her apartment, she would be a good hostess. She gave me tea. Even a few months ago, she said, it would not have been possible to meet her at home, but the authorities "have put on their masks" for the Olympics. She expects a few months of relative latitude before things tighten up for the next June 4 anniversary, then the games. The line has moved, for a time. It will move back.

We talked about the importance of memory and efforts made by people in other countries to accept history, like the German artist who installs small plaques in the sidewalk outside addresses from which Jews were deported to death camps. I told Ding about two exiled Iranian sisters, Roya and Ladan Boroumand, who have created a database of human rights violations as an online memorial to victims of the Islamic revolution. Their father was assassinated in Paris for his opposition to the Khomeini regime. Ding's face drew taut and she made a sound of empathy.

After her son was killed, Ding Zilin went to buy a cake to mark his birthday. A security officer followed her. They waited in silence until the clerk brought out the cake. The icing read, "We miss you." The agent's eyes became wet with tears.

I asked Ding if she would show me where her son was killed. She went to another room to get her glasses. She returned and drew a small circle on my tourist map at an intersection about four miles from the square. Most of the victims were killed on the outskirts as troops rolled in to secure the city. "Muxidi," she said. He was shot in the back while trying to take cover in the entrance to the Muxidi subway stop.

The Tiananmen massacre and the ensuing political crackdown also took a toll on Pu Zhiqiant, a lawyer who works on politically sensitive cases. His participation in the protests at Tiananmen as a youth ruined his chances for an academic career. He says he became a lawyer because he couldn't do anything else. Pu is a broad shouldered man with a crew cut who carries his own tea leaves and thermos in a crocheted bag. "Sometimes I forget I am a lawyer," he says. "I go a little too far.  .  .  .  I feel just as if I was accused."

In 2004, Pu defended two writers who had been sued for libel by a local party official for portraying local party officials in Anhui province as thugs. In an emotional, free-wheeling courtroom argument, Pu cited New York Times v. Sullivan, a landmark American libel case, and the First Amendment to the U.S. Constitution. The case has still not been decided, which in a legal system overseen by the Communist party counts as something of a victory.

Pu told me that one year around the June 4 anniversary, when extra security measures are taken, some agents were assigned to sit in his law office all day. Pu left them in a conference room with a DVD playing The Lives of Others, the Oscar-winning film about an agent of the Stasi, the East German Ministry for State Security, who develops sympathy for the playwright he is spying on. Pu said he felt a little bad that the disc was pirated.

The afternoon the dissidents' letter was released in August, a security official telephoned Liu Xiaobo and asked to meet with him. Because Liu's wife, Xia, doesn't like having policemen in the apartment, they met at a tea house. Liu is in his early 50s, a bit gangly with a short, stubbly haircut and big glasses. In 1989, eager to show intellectuals' support for the demonstrators, he had returned from abroad to join the democracy protests. After the massacre, Liu had been detained for nearly two years. Then again in 1996, he'd been summarily sentenced to three years' "reeducation through labor"--a practice that allows for imprisonment without trial--for signing a letter that criticized President Jiang Zemin.

Liu received me in his living room and study, dark with books and decorated with his wife's paintings and photographs. One of her photographic subjects is dolls with distorted facial expressions. She gave me a stack of her pictures to look through. One of them showed a doll, as if gasping for air, with a sheet of plastic wrapped around its head. "That is from when he was in jail," she said.

I asked about the relationship between the dissidents and their minders. No one I'd spoken with had mentioned any instance of personal cruelty. Most, it seemed, had a story of kindness shown by a member of the security apparatus--though always when no one else was around.

Liu explained the difference between people's public and private face in China's Communist party dictatorship. Privately, people can behave decently. In public, people have to behave in a particular way to protect themselves. Each of the dissidents I met has broken with this convention of the system. All have chosen to merge their public and private selves as much as they can, by signing an open letter, talking freely about the Tiananmen massacre, or meeting me. They are waiting for the line to move far enough that to behave this way--to integrate one's public and private selves--is no longer an act of courage.

One day in Hangzhou, Wen and I had some time to kill. We spent a few hours on a boat on the lake on the west side of town. While our police detail stayed on the shore, Wen told me about a visit he'd had the year before. Liu Xiaobo, the literary critic I'd met in Beijing, and Liu's wife had come to see him. Tailed by police, they went to a scenic lake outside of Hangzhou. There was only one boat, and Wen had already rented it. The policemen came on board. The dissidents and the policemen sat in silence ten feet apart, floating on the water. At lunch later that day, Wen tried to pay the bill and discovered that the policemen had reciprocated for the boat ride by paying the check.

My trip ended without incident. At least, for me. In the months since I returned to Washington, however, two of the people I met but do not mention here have been arrested. I have an idea of what they did to cross the line, but it's hard to know for sure.

Ellen Bork works at the human rights group Freedom House.