Early in 2003, like millions of other migrants of his generation, Sun Zhigang, a young graphic designer, left central China, where he had attended university, and headed for the country’s booming industrial Southeast. His quest: work, and with luck, fortune.

When he entered an Internet café one evening, shortly after his arrival in Guangzhou, he was stopped by police who demanded to see his ID, which he had left behind in his nearby apartment. It was a costly mistake. The police had just launched a large-scale dragnet of illegal migrants, and as was common at the time for people without papers, he was promptly hauled off to detention.

Three days later, Sun Zhigang’s family was informed of his death, which the police claimed had been caused by a heart attack. But the Southern Metropolis Daily, a local tabloid that was just establishing itself as a powerful crusading force in the country’s news landscape, would not let the story end there. A few weeks later, it ran a two-page spread that put a far more sinister spin on the incident. Citing a confidential autopsy report, its bold headline read: UNIVERSITY GRADUATE, 27, SUDDENLY DIES THREE DAYS AFTER DETENTION ON GUANGZHOU STREET.

Word of Sun’s death spread rapidly, so rapidly that what ensued was without precedent in China. Within two hours of the newspaper hitting the street, thousands of people from around the country had posted angry commentary on Sina.com, China’s largest news portal. What would quickly become known nationwide as the “Sun Zhigang case” had begun to go viral.

After its initial scoop, the Southern Metropolis Daily was banned from reporting further on the incident, but old-fashioned censorship measures like this would prove too little, too late. Online discussion of the case was already mushrooming, and so was the scope of debate, which began with calls for justice in one particular tragedy but quickly led to far broader demands for legal reforms to put an end to the arbitrary detentions and other abuses routinely suffered by hundreds of thousands of migrant laborers.

In June, with the Sun Zhigang case still the talk of the Internet, Chinese premier Wen Jiabao announced an end to regulations that police had used for two decades to summarily detain paperless migrants in hundreds of detention centers, which were maintained around the country solely for this purpose.

Beijing has never acknowledged the public fury and Internet mobilization around the Sun Zhigang case as the driver of this major reform, but for most of China’s Internet-savvy public, the connection was unmistakable.

Looking back, China’s Internet era could well be said to have begun with this case. Not literally, of course, since China had been online already for several years. But the outcry over Sun Zhigang’s death is widely seen in China nonetheless as the opening act in the age of the “netizen.” In a country whose populace has been treated as subjects far more than as citizens throughout its history, the emergence of the Internet as a platform for dramatically freer speech, for edgy popular mobilization, for protest and dissent, has arguably given the Communist Party its most serious challenge in controlling the country’s politics since the Tiananmen Square massacre.

At the same time, and somewhat paradoxically, it has also given rise to naïve optimism in the West about the transformative power of information technology. Early on, this optimism caused some, including as prominent a figure as Bill Clinton, to predict that the power of the Internet would irrevocably lead to the democratization of China.

Even while they reject views like these as unrealistic, many analysts of Chinese affairs nonetheless see the story of the medium’s rise there as one of the most important drivers of change in what all by now recognize as one of the world’s fastest-changing societies. They caution, however, that like China itself today, this story is immensely complex, and is unlikely to conform to the scenarios either of the country’s control-obsessed rulers or of those who yearn for a swift democratic transformation of China’s politics.

To understand both the power and the limitations of the Internet under a resolutely authoritarian system of government, it helps to fast-forward from 2003 and the Sun Zhigang case to 2009, to a case that would become just as celebrated as that of the dead migrant worker: the story of Deng Yujiao, a twenty-one-year-old hotel waitress from Hubei Province.

The hotel where Deng worked doubled as one of this increasingly freewheeling country’s countless one-stop spas that offer everything from traditional karaoke, hot baths, and haircuts, to massage and a full menu of sexual services.

Howard W. French is an associate professor at the Columbia University Graduate School of Journalism. From 2003 to 2008, he was Shanghai bureau chief of The New York Times. His latest book, China's Second Continent: How a Million Migrants Are Building a New Empire in Africa, will be released this May. He is currently writing a book about the geopolitics of East Asia.