Long Arm of the Law IV Underground Express (1990)

Following his defeat by Master Ip, Cheung Tin Chi tries to make a life with his young son in Hong Kong, waiting tables at a bar that caters to expats. But it's not long before the mix of foreigners, money, and triad leaders draw him once again to the fight.

An adventure that delves into the dark caverns of the underworld and tells the tale of three chivalrous gangsters who attempt to escape the powerful clutch of their gang leader.

Ko Chow is an undercover cop who is under pressure from all sides. His boss, Inspector Lau, wants him to infiltrate a gang of ruthless jewel thieves; his girlfriend wants him to commit to marriage or she will leave Hong Kong with another lover; and he is being pursued by other cops who are unaware that he is a colleague. Chow would rather quit the force, feeling guilty about betraying gang members who have become his friends.

In the midst of a violent gang war, a series of misfortunes threaten the fate of a gang boss and his mob.

Liu Yue Ping reports to the ICAC about a rich 2G Cao Yuen Yuen who bribed officers of the Hong Kong Correctional Services (HKCS) from inside the prison. William Luk decides to infiltrate the prison as an inmate to conduct his investigation, while his partner Ching Tak Ming and Chief Inspector Lau Po-keung back him up from the outside.

An undercover cop struggling to provide for his son and ailing wife, must infiltrate a ruthless gang. But things turn sour when another cop blows his cover and he quickly finds himself battling for his life and the lives of his family.

Something fishy is going on in the anti-Drug Trafficking Unit of the HK Police, and only a few honest cops know that the corruption goes all the way to the top. However, they must prove their case quickly, and by unconventional means, after they are framed for murder and drug-trafficking themselves. Dodging bullets from cops and criminals alike, the race is on to clear their names, protect their loved ones, and bring their corrupt colleagues to justice.

A police inspector becomes obsessed with apprehending a criminal planning a major heist at the Hong Kong Jockey Club in the weeks leading up to Hong Kong's return to China.

Two detectives who are up to their necks in trouble and in each other's face, as they try to shut down a drug-trafficking scheme that could be connected with international ties to organized crime. But in the midst of their investigation, innocent immigrant dock worker Luk Wan-Ting gets caught up in the mix when he witnesses the murder of an intelligence operative and is framed for the crime.

When his brother is killed, LAPD officer Mark leaves the city to return to the island he grew up on. Seeking answers and ultimately vengeance, he soon finds himself in a bloody battle with the corrupt tycoon who's taken over the island paradise.