Just across the Hong Kong border in mainland China lies the glitzy, hard-edged city of Shenzhen, a boom town to which many young Chinese women come from the poor villages to seek their fortune.
They couldn't go any further even if they wanted to. The former British colony is fenced off from the motherland with razor wire and remains to all intents and purposes a foreign entity for ordinary Chinese people under the "one country-two systems" formula.
Many of the young women go on the town to make money and find a man. They get themselves up in black leather shorts and thick pancake make-up, and totter off on high heels to the flashy new hotels like the Shangri-La. Sometimes they just act as hostesses and sometimes they escort their short-time acquaintances to the cubicles of karaoke bars. The lucky ones find a regular Hong Kong boyfriend. Executive, salesman, truck driver or kitchen hand, it makes little difference; their salaries are all far above those of their Chinese counterparts.
The man is almost inevitably married with a family across the border, but he can afford to set up his mistress in an apartment in that part of Shenzhen known as Heung Biling Village, otherwise known as "Second Wives Village". I found it to be a rubbish-strewn wilderness of condominium towers with weeds growing in unfinished streets. The women living in the high-rise apartments included young factory workers and bright-eyed students. Here they wait, sometimes for days and weeks, for visits from their men. They hang about in hairdressing salons and beauty parlours or play mahjong with other concubines.
Typically a man will pay 8,000 yuan (£900) a month for his mistress to live as a second wife, a fraction of his Hong Kong salary but 10 times the average wage in Shenzhen. Sometimes the second wife leads to a second family. If the child is a boy, joy is unconfined and the proud father comes bearing gifts, before disappearing again. Often the Shenzhen women know about the first family in Hong Kong, but sometimes they don't. A culture of deceit prevails. It was explained to me that the Hong Kong man knows the woman and child in Shenzhen are unlikely to get permission to come to Hong Kong to disrupt his home life there; the mistress in any event has a larger apartment than she could get in Hong Kong and her money goes further in Shenzhen where the standard of living is high in Chinese terms. For their part, wives in Hong Kong probably guess what is happening when their husbands go on business trips, but they may prefer not to know.
And that's how things were until January 29th. Then this whole delicately balanced world was suddenly upset by a court ruling in Hong Kong. The Court of Final Appeal decreed that the children of Hong Kong residents born to women in mainland China were free to come and live in the territory, as could children born in China before either of their parents became Hong Kong residents.
Overnight a mistress in Shenzhen was faced with the prospect of losing her child to the boyfriend's wife, of forfeiting the very baby which was a means of ensuring that the man stayed with her. The man was faced with the fact that his Shenzhen son or daughter was free to live and work in Hong Kong if they wished, and could come knocking on his door. The decision has not just panicked such men and their concubines, it has also provoked a storm at a higher level, and has become the first constitutional crisis since the hand-over in July 1997. A Beijing cabinet minister said it was a mistake which violated the Basic Law, Hong Kong's post-colonial constitution. Chinese legal experts said the ruling challenged decisions made earlier by China's parliament, which blocked such children from gaining Hong Kong residency.
This was seen in Hong Kong as a dangerous affront to the territory's legal and judicial independence. Mr Martin Lee, leader of the Democratic Party, said that if the Chinese parliament overruled the decision, "then there goes rule of law in Hong Kong".
Already confidence in the Hong Kong judiciary had been shaken by the recent failure of the Secretary for Justice, Ms Elsie Leung, to prosecute Hong Kong newspaper tycoon Ms Sally Aw Sian, three of whose executive colleagues were jailed for falsely inflating circulation figures on her orders. Critics said this was cronyism and opened the door to one law for the rich and well-connected, and another for the poor. The decision to admit immigrants came about because the law was challenged by several illegal immigrants in Hong Kong. They claimed the right to stay because one parent lived in the territory. But now many of the women living in Second Wives Village are unhappy about what such freedom might mean for them. As one Shenzhen resident said, opening the door a little into Hong Kong might cause more unhappiness than the judges could ever imagine.