The film is set in Hong Kong where a young man becomes a bodyguard and befriends a mercenary determined to begin life anew with the woman he just married.

The film was re-written several times during production and post-production stages to accommodate director Tsui Hark's casting choices.

During an alcohol-fueled night, drunk Tyler Yim impregnates inebriated Ah Jo, a lesbian undercover cop who had gone to the bar after a fight with her girlfriend.

He joins an unlicensed bodyguard service led by Uncle Ji to earn money to give to Ah Jo, who wants nothing to do with him.

A group of mercenaries from South America, known as the Angels, arrive and threaten Jack, who they call Juan, and their second in command Miguel Joventino offers him a chance to rejoin them if he kills his own father-in-law.

Jack drops his wife off at her father's mansion, giving her a key to a train station locker and telling her to go there when their child is born.

Tyler ends up trapped in the apartment with the gas leaking and only manages to survive the explosion by hiding in the refrigerator, on the advice of Jack.

The police, still suspicious of Tyler from earlier, place him at the scene of the gun battle and explosion and send a Special Duties Unit team after him to the station.

In a confrontation on railroad tracks, Jack saves the life of a SDU team lieutenant by killing one of the Angels and surrenders to him.

Tyler has to hunker down in the tunnels as Ah Hui starts to give birth, and Jack convinces the SDU Lieutenant to let him go after Miguel in the stadium.

Wu's character was rewritten with him in mind by making him more of a sad loner to match the music he made with his band in China Blue.

He reorganized the entire script including cutting many of Nicholas Tse and Anthony Wong Chau Sang's scenes, leaving Wu Bai's sequences as they were.