Indeed, triads and the police officers chasing them are now in throwback time after the killing in Tsim Sha Tsui 18 months ago of a leader of one of Hong Kong's most feared triad societies, the Sun Yee On, apparently by members of another big gang, the Wo Shing Wo.

There is major concern that this vendetta involving two rival "dragon heads" - triad bosses - has a way to run, so for more than a year gangbusters and other police officers have been on a constant state of high alert for rumblings.

One basic and worrying indicator: the number of reported midnight fights - with triad hands in most of them - soared 30 percent last year over 2009.

Police, of course, have always been well aware that the tradition-bound gangsters had not gone away just because years of very public bloodletting eased off in the 1970s. The most efficiently organized triads just changed some ways of doing crime business in tune with the reshaping of Hong Kong.

Certainly the officers fighting gangsters have never been short of action, facing tens of thousands of triads belonging to scores of societies.

[No one quotes numbers with certainty, and the police force is unwilling to reveal the manpower it commits to anti-triad efforts. But membership of triad societies is certainly much greater than the overall police strength of 35,000. The five big societies are thought to have memberships of at least 20,000.]

Fears of more revenge killing have seen the Organized Crime and Triad Bureau and the Criminal Intelligence Bureau step up countermeasures and arrest 11 senior leaders from the Sun Yee On and the Wo Shing Wo in recent times, while others have fled.

For while no one has replaced 41-year-old ex-boxer Lee Tai-lung as Sun Yee dragon head after he was killed in a "ram-and-chop" hit outside the Kowloon Shangri-La Hotel in 2009, officers are not waiting to hear another feared gangster is in his place before they try to prevent more very public killings.

A vital strategy in nabbing leaders is infiltrating crime groups. "Police have in recent years organized an extensive network of undercover cops to collect enough evidence to arrest key triad members," an investigator with an operational unit told The Standard's sister publication, Eastweek magazine.

Yet if officers worry about more acts of revenge, they also see opportunity in the absence of a replacement for the murdered Lee to at least set back, if not neuter, some triads.

"This is a golden time to carry out large-scale operations to impede their expansion and destroy their main sources of income," the investigator added.

"On the other hand, we want to warn the main gangs to stop the bloodshed or from seeking revenge."

In fact, police figures suggest the force has been getting on top of triad activity overall. There were 1,645 crimes listed as "triad related" last year, down 14 percent on 2009. And triads were held responsible for 2.6 percent of all crime last year compared with 3.8 percent a decade ago.

Today, Sun Yee On and Wo Shing Wo, which control Tsim Sha Tsui and Tai Kok Tsui in Kowloon respectively, have two of the most feared networks in Hong Kong along with the 14K, Wo Hop To and Wo Shing Tong.

Main sources of income are illegal gambling dens, money-laundering, prostitution and drug trafficking.

Shopowners in areas troubled by triads can face a demand for HK$100,000 for "protection," says the owner of a restaurant in Tsim Sha Tsui.

Basic triad business is reflected in crimes with which the 11 senior triads arrested in the past 18 months - six from Sun Yee On, five from Wo Shing Wo - have been charged: money laundering and illegal bookmaking, along with membership of a crime group.

Bloodstained machetes

Other police action to crimp ideas of revenge include a raid on a private club operated by Sun Yee On in Tsim Sha Tsui last January, when two bloodstained machetes were among items seized. The 24-year-old club operator was charged with possessing weapons.

In November, a rising leader of Wo Shing Wo nicknamed "Little B" was arrested for operating brothels and money laundering involving an estimated HK$380 million.

A month later the Organized Crime and Triad Bureau raided more than 20 private clubs, which led to the identification and arrests of two senior members of the Sun Yee On who had been close to its murdered dragon head.

Wo Shing Wo is reckoned to have been less active since police started pushing hard.

Although its dragon head, "Tattooed Chung," is on the run - believed to be in the mainland - three reputed senior leaders were among those arrested last year for illegal bookmaking, human trafficking and being members of a triad society.

Police pressure was also applied, with several raids last year on an underground casino in Tai Kok Tsui, one of Wo Shing Wo's main sources of funding.

Insights into the underworld have been presented in the High Court, with five people on trial in connection with the killing of Lee Tai-lung, a "double flower red-pole" fighter as well as a dragon head. The five - alleged members of the Wo Shing Wo and aged from 23 to 50 - have pleaded not guilty to murder, conspiracy to wound or assisting in murder.

Lee was hit by a van outside the Kowloon Shangri-La on August 4, 2009. Then, in an attack that lasted only 30 seconds, three hooded assailants slashed with knives at his motionless body.

The motive for the killing was said to be revenge because Lee disfigured Sun Yee On boss Leung Kwok-chung - aka Tattooed Chung - in a bar brawl three years earlier.

A Lee associate, the immunity- enjoying Man Pui-ying, said that when a dispute erupted in a lounge in Tsim Sha Tsui in July 2006 his boss summoned 20 "brothers" to fight back. Their rivals also called in a score of reinforcements.

Tattooed Chung was smashed by Lee with a whiskey bottle, which left him with a scar on his face and neck. And Lee was supposed to have heard someone say Tattooed Chung would seek revenge.

Manchu rebels

Triads have existed for hundreds of years in China, composed initially of rebels who opposed Manchu rule and eventually branched out in the mid- 1700s into several groups, including the Three Harmonies Society, which had a triangle as its emblem.

British authorities in colonial Hong Kong dubbed the groups triads because of that symbol.

Chu Yiu-kong, an assistant professor of sociology at the University of Hong Kong, the author of the academic tract Triads as Business and a founding member of the Hong Kong Juvenile Delinquency Research Society, says there were once more than 300 triad societies in the territory, most established between 1914 and 1939.

Around 50 societies exist in Hong Kong today, he adds, and 14 of them regularly come to police attention.

One reason for the drop, he says, was the enactment of the Societies Ordinance in 1949 to outlaw triads. It stipulates that anyone convicted of claiming to be a triad officer bearer or managing or assisting in the running of a society can be fined up to HK$1 million and sent to prison for up to 15 years.

Being a member of a triad can bring fines up to HK$250,000 and three to seven years imprisonment.

Luk Kai-lau, a retired police officer, notes that the influence of triads in Hong Kong has waned since the 1970s, when he was a frontline officer.

"Those were the days when curbing triads was one of the big challenges to law enforcement here. Running brothels was their most lucrative business," said Luk.

"The problem was worsened by the corruption of police. Inspectors had a lot of power in districts, and it was common for them to associate with gang leaders in getting money."

That changed after the Independent Commission Against Corruption was established in 1974. Triad turf control was weakened and "some gang societies shifted their sources of income to underground dealings and then legitimate businesses." That, Luk said, included entertainment.

Now, though, the clock could be turned back to the business of blood and terror.