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.

This sequel to the critically-acclaimed box-office winner Long Arm of the Law maintains the same stark realism of the original. In Saga Two, the Royal Hong Kong Police put into operation a new plan to counteract the problem of increasing violent crimes committed by new arrivals from across the border in China. In agreement with Chinese authorities, three Hong Kong detectives go undercover as illegal immigrants in order to infiltrate the powerful gang that is organizing the crime wave. The action is tough and graphic, reminiscent of The French Connection, Hong Kong style.

In the crime-infested Kowloon Walled City of Hong Kong, a group of undercover police officers take on the challenge of infiltrating a powerful criminal organization. As they navigate the treacherous world of drugs, violence, and corruption, the officers risk their lives to bring down the criminals and restore peace to the city.

Michal Mak's second sequel to his brother's action classic finds an ex-soldier/escaped death row prisoner fleeing to Hong Kong and forced to work for a gang of criminals when they kidnap the woman he loves.