BANGKOK • China's increasing assertiveness in South-east Asia may well have taken an ominous new direction. It's not just oil rigs off the shores of Vietnam or artificial islands being built near the Philippines in the South China Sea.
Most places, you worry about bookstores vanishing. Sadly, in Hong Kong and now Thailand, it's also booksellers. And that's not good news for South-east Asian business people at home and in Hong Kong. The capitalist, freewheeling city-state has been pretty much left on its own to run as an autonomous special administrative region of China since the British left this one-time Crown colony in 1997.
That could now be changing.
As China's gross domestic product (GDP) growth rate slows to 6.9 per cent - the slowest in a quarter century - more attention may well be placed by the authorities in China on stomping out anything that could trigger questions about their leadership and ability to run the nation.
In an unfolding tale that reads as if it's from a Cold War spy thriller, Gui Minhai, a Swedish national born in China, went missing last autumn from his condominium in the Thai city of Pattaya on the Gulf of Siam. Four of his colleagues also disappeared.
One, Lee Bo, vanished at year's end from Hong Kong, the home base of their publishing company Mighty Current Media and its retail arm Causeway Bay Books.
Mighty Current has specialised in part in publishing and marketing controversial books, often highly critical of China's communist leadership. Mr Gui and Mr Lee's other three book-publishing colleagues reportedly disappeared while in mainland China.
Mr Gui has since re-emerged on China's government-run state broadcaster CCTV. In a tearful broadcast confession, he said he had returned to China to face justice for his involvement in a 2003 fatal hit-and-run accident in the city of Ningbo. His family and friends are sceptical and wonder if the filmed statement was coerced.
Also, according to media reports, the public security authorities in Guangdong, which neighbours Hong Kong, have confirmed they are holding Mr Lee, a British passport holder. He disappeared from Hong Kong on Dec 30.
Local Hong Kong media is reporting that a letter Mr Lee purportedly wrote to his wife said he has "voluntarily" returned to China "to assist with an investigation".
There is no word yet on the whereabouts of Mr Gui and Mr Lee's three missing colleagues: Causeway Bay Books manager Lin Rongji, general manager Lu Bo and staff member of the publishing house and book shop Zhang Zhiping.
Rumours are flying. A leading theory focuses on Mighty Current's possible publication of a tell-all book on the twice-married Chinese President Xi Jinping's alleged love affairs. Such a book, with its possible hint of hypocrisy amid Mr Xi's ongoing crackdown on corruption and other behaviour not deemed appropriate by the Chinese Communist Party, would have incurred the ire of China's ruling elite. Mighty Current's titles are banned in mainland China where the news media and publishing industry are tightly controlled.
This time, as the rumours - and conspiracy theories - go, Mighty Current's plans may well have spurred Mr Xi to send Chinese security forces across the border to spirit away the Swedish and British passport holders to China against their will. That's one way of trying to stop a publication: get rid of the booksellers, editors and publishers before the book is even done.
"An upsurge in cases of possible enforced disappearance in China in the context of an ongoing crackdown on dissent is deeply worrying," the global writers' organisation PEN International said in a statement released earlier this month. "Since November 2015, five Chinese writers, publishers and booksellers have disappeared in China and Thailand and PEN believes that it is highly likely that they are detained by the Chinese authorities in conditions amounting to enforced disappearance."
More intrigue will no doubt follow. The Swedish and British authorities have raised questions about treatment of their respective citizens. The hashtag #bookseller has emerged on Twitter.
In Hong Kong, the disappearances have brought some protesters back to the streets. Democracy activists are calling on Hong Kong's Chief Executive Leung Chun Ying to better defend what seems to be an increasingly troubled "one country, two systems" form of autonomy.
In Thailand, on the other hand, there seems to be little discussion of what may well be viewed, if known at all, as the disappearance of a visiting foreign citizen.
Mr Steve Herman, South-east Asia bureau chief of Voice of America and a long-time Asia reporter who now resides in Bangkok, noted: "A critical unanswered question is whether there was collusion between the Chinese government and Thai authorities. The lack of concern expressed by the ruling military junta is notable." He added: "China has demonstrated that it has the long reach to apparently abduct people beyond Hong Kong, including here in South-east Asia."
Relations between Thailand and China remain strong. Despite China's slowing growth rate, the nation overtook Japan in August last year for the first time as the source of the largest amount of foreign direct investment in Thailand, and Chinese tourists have come to dominate the visitor numbers.
As an indicator of the close relationship, the Thai government had, despite international outcries, deported more than 100 Uighur Muslims back to China last July, and more recently two Chinese dissidents awaiting United Nations repatriation to a third country.
A climate of fear may well come should it be confirmed that mainland Chinese security forces have abducted people from the streets of Hong Kong and Thailand. But, until then, business goes on - if not quite the rule of law.
The impact of China's slowing economic growth is likely the greater daily concern in both Hong Kong and Thailand, still the second-largest economy in South-east Asia, after Indonesia.
Yet, the tale of the missing booksellers should give reason to pause. It's no longer just the pollution that can be dangerous to your health when doing business with or about the Chinese.
Both Hong Kong and Thailand's leaders should recognise that acquiescing or turning a blind eye to "enforced disappearances" can never be good for business and economic growth in the long run.
The writer, a former United States ambassador to the Asian Development Bank, is managing director of advisory firm RiverPeak Group.