GUI Minhai was the first to disappear.

A Swedish citizen of Chinese birth, he vanished from a Thai holiday resort in October.

The incident might have escaped notice outside of his family if not for Mr Gui’s job — and the fact that, one by one, his colleagues would also begin mysteriously disappearing.

Mr Gui is a book publisher with a controlling interest in a small but popular bookshop in Hong Kong.

To date, five men linked to the store have gone missing, sparking widespread conspiracy theories and calling into question the true level of autonomy enjoyed by Hong Kong under Chinese rule.

The mystery has captured the imagination of the population, sparked protests and even attracted the attention of the Hong Kong branch of the Anonymous hacker group.

Most theories suggest that Chinese government operatives are behind the disappearances in an effort to censor the bookstore, which sells unflattering and often salacious books about China’s ruling elite. At the time people began dropping off the face of the earth, the store was planning to release a book about a former girlfriend of China’s president Xi Jinping.

In the latest twist, a handwritten letter was published by Taiwan’s Central News Agency on Tuesday which it claimed was written by publisher Lee Bo, who disappeared last week.

“I am very well. Everything is fine,” he wrote in the letter addressed to his wife.

But a closer look at what’s really going on shows clearly everything is far from fine.

THE ‘INSIDE STORY’

Tucked away between a pharmacy and a clothes shop, Causeway Bay Books is notorious for its offerings that take aim at China’s ruling party. Stocked titles include The Collapse of Xi Jinping in 2017 and The Inside Story of the Big Explosion in Tianjin.

Many of the books contain gossip about the private lives of China’s elite, including Communist Party leaders, and are popular among mainland Chinese tourists.

But after employees and stakeholders began one-by-one to disappear, the store now sits padlocked and closed.

Gui Minhai owns Mighty Current, a publishing business which controls the bookshop and was the first to go.

Mr Gui went missing in October from a holiday resort in Thailand. He has contacted his family since disappearing, but they say they have no idea where he is or why he is unreachable. His phone calls to the family are diverted through foreign countries, the Guardian reports.

In the same week, three other men linked to the store also disappeared.

They included the publishing house’s general manager Lui Bo, business manager Cheung Jiping and store manager, Lam Wing-kei.

On December 30, Lee Bo joined the list of missing men after he failed to return home from a visit to his warehouse in Hong Kong. His wife told local media that he called to tell her he was “assisting with investigations” on the day he disappeared. She said the call came from the Chinese city of Shenzhen, despite the fact that he didn’t take his mainland travel permit and there is no record of him crossing the border.

The nervous tone of Lee in the phone calls led her to lodge a missing person’s report which she rescinded on Tuesday following the publication of the letter from her husband that was reportedly faxed by Lee to a colleague on Monday.

“It might take a bit of time,” the message said. “My current situation is very well. All is normal.”

A friend of Lee who volunteers at the book store and did not want to be identified told reporters that Lee’s “wife is on the brink of collapse.” He added he too was afraid for his safety.

“I feel unsafe — I don’t know whether the next one will be me,” he said.

It has since emerged that Mr Lee is a British citizen and UK officials have joined the chorus of those calling for answers.

“We have urgently inquired with both Hong Kong and mainland authorities,” British Foreign Secretary Philip Hammond said while on a visit to Beijing.

Swedish authorities have also made public statements saying they are taking the matter “very seriously”.

“Swedish law enforcement authorities are working on the case. Our embassy in Bangkok has raised the issue with high-level Thai representatives,” spokesman Gabriel Wernstedt told the South China Morning Post.

For their part, Hong Kong police say they are trying to get to the bottom of the mystery. “Police are doing their best to investigate the issue,” Hong Kong’s chief executive, Leung Chun-ying, said on Tuesday

China, however, remains characteristically tight lipped.

Missing Hong Kong Bookseller's Letter Raises Suspicion Days after the disappearance of Lee Bo, a co-owner of a Hong Kong bookstore selling titles critical of the Chinese government, a letter emerged that appears to be signed by him. This has offered more questions than answers. Photo: Getty

A FIRESTORM BREWING

There has been speculation in the past of China interfering with the politics of Hong Kong, but it is the first time that residents are rumoured to have been abducted from the territory by mainland agents, according to the The Economist.

The political fallout from the widely held belief that the Chinese Communist Party is responsible threatens to dramatically sour the relationship between the people of Hong Kong and the mainland government. The situation could very likely prove to be a turning point in the political arrangement since Britain returned the island to Chinese rule in 1997.

Hong Kong is part of China, but under the principle of “one country, two systems” it maintains its own legal, political and economic apparatuses.

The book store case has sparked fury among lawmakers and activists in Hong Kong, adding to growing unease that freedoms in the city are being eroded.

The Hong Kong division of hacker group Anonymous has also vowed to hack Chinese government websites in retaliation for the kidnappings.

“We cannot tolerate the China police who violated the section ‘One Country Two Systems’ and robbed those five Hong Kong citizens,” a figure behind a Guy Fawkes mask said in a video posted online.

Amid protests and public demonstrations by supporters and pro democratic advocates, Hong Kong’s Chief Executive Leung Chun-ying called a hastily-organised press conference Monday in an order to address the growing unrest.

He said that he was “highly concerned” about the recent disappearances of people associated with a publishing company but told reporters there’s no evidence so far to support suspicions that mainland security agents were involved.

Leung, who is often derided as a puppet for Beijing, said there is “no indication” the mainland was responsible.

“If mainland Chinese law enforcement personnel are carrying out duties in Hong Kong, it would be unacceptable because it goes against the Basic Law,” he said.