Chasing the Dragon, Jackie Pullinger

Until it was pulled down, the Walled City was Hong Kong's most foreboding territory. It was a lawless place, dominated by the Triads, and which the police hesitated to enter. Strangers were unwelcome. Drug smuggling and heroin addiction flourished, as did prostitution and pornography, extortion and fear.
When Jackie Pullinger set sail from England in 1966 she had no idea that God was calling her to the Walled City. Yet, as she spoke of Jesus Christ, brutal Triad gangsters were converted, prostitutes quit, and Jackie discovered a new treatment for drug addiction: baptism in the Holy Spirit.