The best Dion Lam Dik-On’s thriller movies

The plot includes the plight of two women who both find themselves betrayed by the men they love. It's a violent female 'buddy' movie, with two mismatched heroines, a policewoman (Cheung) & a drug addicted prostitute(Guo) joining forces to gain revenge.

Chen is a dedicated social worker who has allowed her job to dominate her personal life. Inadvertently, she neglects her devoted husband Lo-Wei and their young son. Although he dislikes his wife's patients ("they're just street trash"), Lo-Wei is tolerant of his wife's workaholic situation and he takes the opportunity to develop a strong unity with his son, Chia-Pu. Then, Lo-Wei's sister offers to babysit the child while the parents respond to an emergency case. While they're gone, one of Chen's "delinquents" breaks into the house and rapes the sister. During the assault, baby Chia-Pu climbs out of the window and falls to his death. Lo-Wei is over-the-edge with grief. His brain snaps. He withdraws into himself, except at night when he stalks the "street trash," gruesomly killing them...

A cop suffering from "posterior ulcers" tries to catch a serial killer who seeks out victims with medical problems. One suspect is a man who makes pies from guts, which the cop inadvertantly eats. Eventually the hero cop finds himself tied to an operating table with the killer preparing to deal with his "posterior ulcers"!