A Scanner Darkly

Substance D - otherwise known as Death - is the most dangerous drug ever to find its way on the black market. It destroys the links between the brain's two hemispheres, leading first to disorientation and then to complete and irreversible brain damage. Bob Arctor, undercover narcotics agent, is trying to find a lead to the source of supply, but to pass as an addict he must first become a user?