An undercover narcotics agent tasked with infiltrating a drug ring finds his own identity fracturing as he becomes addicted to the very substance he is investigating. Bob Arctor, operating under the pseudonym Fred, navigates the paranoid, surveillance-heavy landscape of near-future Los Angeles while attempting to track the distribution of the lethal drug Substance D. As he spends more time among the addicts he is assigned to monitor, the cognitive decline caused by the drug begins to erode his sense of self and his ability to distinguish his mission from his addiction. The narrative utilizes a shifting, often disorienting perspective to mirror the protagonist's deteriorating mental state, trapping the reader within the same uncertainty that plagues Arctor.

This work is widely regarded as one of the most personal and harrowing explorations of addiction in the science fiction genre. Critics often highlight how the narrative effectively captures the psychological erosion caused by substance abuse through its unstable, shifting prose. The story is frequently cited for its prescient commentary on surveillance culture and the loss of individual autonomy in a society obsessed with control. Readers often note that the book avoids moralizing, instead presenting a raw and clinical look at the disintegration of a human mind under the influence of a destructive chemical agent.