Xiao Jianhua is not just an extremely rich man who was abducted by Chinese public security agents and taken from Hong Kong to mainland China. He is also a Canadian citizen.
What happened to him could conceivably happen to any Canadian, or anyone in Hong Kong. The rule of law, based on British institutions, is still supposed to govern the city. But Beijing's security authorities do not fully accept the treaty guarantee of Hong Kong's distinctness, known as "one country, two systems."
Mr. Xiao may be the first Canadian to discover that, when Chinese police want someone, the Hong Kong-China border does not exist. But he is not the first resident of Hong Kong to learn this.
In 2015 and 2016, there was the tortuous saga of the Hong Kong booksellers and publishers. Several dealers in books and magazines featuring gossip about and exposés of mainland Chinese political figures were abducted by Chinese authorities, as an encouragement to close down their operations. In due course, they all did.
So far, everyone abducted appears to have been a Chinese citizen, a Hong Kong resident, or a dual national of China and another country. (China does not recognize dual citizenship.) But given that Chinese police have been willing to ignore the border line, there's reason to worry that anyone in Hong Kong, visitor or resident, risks being detained by Chinese authorities. It undermines the thing that has given Hong Kong its exceptional level of liberty and economic success: a distinct and independent legal system.
As for Xiao Jianhua, he was at one time a student radical in China, but his family is well connected with that of Xi Jinping, the paramount leader of China. Mr. Xiao was reportedly living in a lavish apartment in Hong Kong's Four Seasons Hotel, and he was arrested just as the Chinese Lunar New Year was beginning. It's now vaguely said that he's "assisting investigations" about stock market turmoil in 2015.
C.Y. Leung, the Chief Executive of Hong Kong, is retiring. Regina Ip, one of the candidates to succeed him, has said that the case of Mr. Xiao shows there is a need for an extradition agreement between Mainland China and Hong Kong. Maybe, but the city's liberalism could suffer from even more ties to the mainland. The rule of law in Hong Kong is fragile enough as it is.