The Association.

Plain-clothes detective Wang is the best in his trade. One day he stumbles across a young girl's body who apparently is died of abortion. Wang investigates the guilty abortionist who leads Wang to a secret organization called "The Welfare Association". Actually it is an international prostitution racket. Wang sneaks into the association. When he is about to arrest the association's organizer, a girl, Lei, whose sister's death cause by the secret society, saves Wang in certain death. Wang arrests the organizer but has set her free from headquarter. Wang and Lei get together in getting the commander dismissed.