The final entry in Michael and Johnny Mak's Long Arm of the Law series, Underground Express once again tells a story of gangsters versus police, focusing on the difference between how both factions act depending if they're coming from Hong Kong or Mainland China.

The story of Ho, a Chinese peasant/slave worker who escapes to Hong Kong and becomes one of the most feared gang bosses in Hong Kong.

After an aspiring comic book artist rescues a young girl from a prostitution ring, he submits to the teachings of an aging kung fu master in order to take on the local mob boss' son: a deadly assassin who's a master of the scorpion kung fu technique.

In 2001, where all correctional facilities have been privatized, martial artist Ricky finds himself victim to the corrupt system, found "guilty" of the manslaughter of an infamous crime boss.

In an effort to get his buddy out of a gambling debt, Jeff agrees to join forces with Judge in a weapons heist. The job goes bad and Judge betrays Jeff. Jeff plots the ultimate revenge on Judge and his followers and it is a question of whether he can follow through with his plan.

Suen makes a living by selling fish-balls and being a nice likeable guy. One day he accidentally gets caught up in a police chase where a pregnant woman gets killed. A dirty cop frames Suen for the death and he gets sent to jail. When he is released from jail he goes to live with his brother. The next door neighbour is a pretty woman (Rosamund Kwan) who Suen starts to like. Unfortunately it turns out that she has a boyfriend and guess who it is? Yes, it is the dirty cop that framed Suen! Their conflict keep escalating until it starts to turn deadly and it all ends in a last duel!