Imagine, for a moment, how it might sound to turn on the news one day and hear that the head of the A.C.L.U. had vanished from his home in the predawn hours. Or, think how America might be different today if a pesky young Thurgood Marshall had been silenced using an obscure tax rule and kept out of the courts.

At around 5 A.M. on Wednesday, Chinese authorities visited the home of Xu Zhiyong, a prominent legal scholar and elected legislator in Beijing, and led him away. He has not been heard from again. Unless something changes, he is likely to stay away for a long time, with or without formal charges. Anyone with an interest in China, its economy, its place in the world, or the kind of future it will fashion, please take note: this is a big deal.

Xu might not have reached Marshall status yet, but he is as close as China gets to a public-interest icon. He teaches law at the Beijing University of Post and Telecommunications. He has also run the Open Constitution Initiative, a legal-aid and research organization that worked on many of China’s pathbreaking cases. He and his colleagues had investigated the Sanlu milk scandal, in which dangerous baby formula harmed children’s health, and assisted people who had been locked up by local officials in secret undeclared jails. All of those activities are emphatically consistent with the goals of the Chinese government, even if they angered the local bureaucrats who were caught in the act.

Xu has never set out to undermine one-party rule; he is enforcing rights guaranteed in the Chinese Constitution. He has enough faith in the system that he joined it: in 2003, he ran for and won a seat as a legislator in his local district assembly, one of the few independent candidates to be elected in an open, contested election. He even received the recognition, rare among activists, of being profiled last year in a Chinese newspaper. “I have taken part in politics in pursuit of a better and more civilized nation,” he said at the time. “I am determined to prove to the citizens across the country that politics should be desirable.”

His work naturally angered parts of China’s bureaucracy, and pressure on him mounted. On July 14th, the Open Constitution Initiative, also known as Gongmeng, was fined 1.42 million RMB for “tax evasion.” Then it was banned. Xu was to have had his day in court, except he was picked up before he could. Separately, a young colleague named Zhuang Lu has also been detained, and her whereabouts are unknown. It is easy to look at China’s list of high-profile detentions and rationalize them: that guy was a cowboy, or, things in China are improving, and we have to keep it in context. Sorry. Not this time. Xu is no cowboy. As a Time magazine reporter wrote, in 2007, “Xu is probably the person most committed to public service that I’ve met in China, and possibly in my whole life.” Moreover, his work is as intimately connected to the broader context of China’s economic and political future as you can get. When the U.S. and China wrapped up a round of strategic and economic talks this week, they issued a joint press release that affirmed “the importance of the rule of law to our two countries.” Hu Jintao is quoted every chance he gets—“the rule of law should let the people be the masters of the country”—talking about exactly the kind of legal professionalism that Xu stands for. Jeffrey Prescott, the deputy director of Yale’s China Law Center, which has worked with Xu and his organization since 2004, tells me:

He is doing careful, thoughtful, and important work of international caliber—not much different than what mainstream public interest lawyers and scholars do every day in the U.S. or anywhere else. Xu and his colleagues are doing research into China’s problems, making efforts to promote constructive ideas for legal reform, and helping provide legal assistance to weak and marginalized groups in society…. Any of this would make Dr. Xu an important figure. But, above all, it is his human qualities that make him truly compelling. He is someone of rare idealism, judgment, commitment to law, selfless dedication, and fundamental decency. So that makes his detention very hard to understand.

For China, and those who have given their careers to studying and negotiating with it, this is a big test. It’s not too late for Xu to be released before the full bureaucracy gets too invested in holding him, but time is limited. China deserves better than this kind of behavior. Xu—or Hu Jintao—would be the first to tell you that.