UCOK wears a denim jacket all day, despite the intense Jakarta heat. He doesn’t want people to see the scars on his arms. A quietly spoken 29-year-old, Ucok is an outreach worker for drug addicts in Jakarta’s most densely populated slum, Tambora. He knows the place well. Until six years ago he was a heroin addict too.

Tambora has the highest incidence of HIV/AIDS in Southeast Asia, and the rate of infection is growing. In the last 10 years t