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...