Britain has waded into the swirling mystery surrounding Hong Kong's missing booksellers, with one of them - Mr Lee Bo - identified as a British citizen.
British Foreign Secretary Philip Hammond, who is visiting Beijing, told reporters yesterday he has raised the issue of Mr Lee's disappearance with his Chinese counterpart, Foreign Minister Wang Yi.
Mr Wang did not reply directly when asked if China had detained the booksellers, but said its policy towards Hong Kong remained "unchanged". "We will continue to uphold the principles of 'one country, two systems', Hong Kong people administering Hong Kong, and a high degree of autonomy," he said.
Asked if China would recognise Mr Lee's British passport, he said: "Based on the Basic Law of Hong Kong and China's nationality law, this person in question is first and foremost a Chinese citizen."
Mr Lee, 65, a partner of Hong Kong publishing firm Mighty Current, which specialises in political titles about China's leaders, was reported by his wife Sophie Choi to have disappeared from Hong Kong last Wednesday. Hong Kong was spooked, with lawmakers and analysts worried he could have been snared by mainland agents and spirited off to Shenzhen.
He could not have gone willingly. In recent times, we have been so scared, we don't dare to go to the mainland.
MS SOPHIE CHOI, on the disappearance of her husband, Mr Lee Bo
Chief Executive Leung Chun Ying has stressed that it is unconstitutional for other law enforcement agencies to make arrests here.
Mr Hammond said he hoped any charges against Mr Lee will be brought against him in Hong Kong.
But the plot thickened yesterday, with Ms Choi saying she now believes her husband had travelled to the mainland voluntarily. She had received a handwritten note from him on Monday saying he is there to handle an urgent matter that others cannot know.
The note is genuine, she said, and she has retracted a police report she made. It was a volte-face from her frantic response earlier.
On the night of his disappearance, Mr Lee had called his wife from a Shenzhen number, saying he was helping in an "investigation". But his Home Return Permit, the document for Hong Kongers to go to the mainland, was at home, meaning that he had entered the mainland via unofficial channels.
"He could not have gone willingly. In recent times, we have been so scared, we don't dare to go to the mainland," Ms Choi told local news website Initium Media earlier.
There was a good reason for that caution. In October last year, four of their colleagues disappeared: Mighty Current majority shareholder Gui Minhai vanished during a holiday in Thailand; Mr Lu Bo, the general manager, and Mr Lin Rongji, the bookstore manager, disappeared in Shenzhen; and retail manager Zhang Zhiping disappeared in Dongguan city near Shenzhen.
The quintet were running a dangerous trade in books banned on the mainland for their "explosive" content, chronicling the latest power struggles or gossip about the personal lives of Chinese leaders.
Mr Gui and Mr Lee had set up Mighty Current before buying over Causeway Bay Bookstore in 1994. Chinese tourists flocked to it, clandestinely stashing the books in their suitcases.
There are other bookstores selling such material, but Mighty Current publishes its own material as well. Among the four or five such publishers in Hong Kong, Mighty Current is the biggest, contributing about 30 per cent of output, estimates China specialist Willy Lam.
It is profitable, with quick cashing in on controversies such as the feuds between former president Jiang Zemin and current leader Xi Jinping, says Democratic Party lawmaker Albert Ho. Important works are also published, such as The Private Life Of Chairman Mao, written by his doctor Li Zhisui.
It is a lot less entertaining for Beijing, which has taken action against Hong Kong's publishers.
In 2013, Morning Bell Press chief editor Yiu Man-tin, then preparing a book on Mr Xi, was nabbed in Shenzhen after receiving a call from a friend there to deliver paint to him. He was sentenced to 10 years in jail for smuggling.
Softer methods were also used: Sources say there were at least two instances where publishers were offered payments of up to HK$1 million (S$184,000) by Chinese security agents to stop publishing certain material. They accepted.
But Mr Lee's case is the first where someone apparently disappeared from Hong Kong itself. It is unclear what could have led to it. The offending issue was likely a new book called Xi Jinping's Lovers, says Dr Lam, citing sources - a subject bound to rile the Chinese leader whose marriage to glamorous folk singer Peng Liyuan has softened his image in China and overseas.
It is believed that Mr Gui has been detained by the Chinese and that he had ordered the printers to stop the publication. And Mr Lee had felt safe in Hong Kong, said his wife. "He said, 'How can anything happen in Hong Kong? So many people on the streets, how will they abduct anyone?'"
But "they" did, apparently.
Under the Basic Law and the "one country, two systems" framework, only Hong Kong enforcement agencies are allowed to take action in the city. But such niceties are no longer of any consideration to Beijing, reckons Dr Lam. "Xi's policy towards Hong Kong has hardened. He is turning the screws tighter to create a chilling effect."