by Evelyn Nieves

About the author: Evelyn Nieves is a reporter for the New York Times.

On January 8, 2001, at 5 A.M. in San Francisco's seedy Tenderloin area, the drug addicts are just about the only ones out.

A young woman with matted blond hair stumbles down the street with her eyes closed; a man in a red spandex dress and silver pumps nods out against the door of a single-room-occupancy hotel; small clusters of hollow-eyed men and women hover on corners. It is no wonder the police call this strip of the Tenderloin the heroin corridor. Everyone on the street looks either high or hung over.

Later in the day, Matt Dodman, a blond, angelic-looking 26-year-old, is sitting in a cafe in another, hipper neighborhood, the Mission. A heroin user for three years, he avoids the Tenderloin drug scene...