An undercover narcotics agent attempting to infiltrate the Southern California drug subculture to find the source of Substance D. Living a double life, he resides with heavy drug users while reporting to his superiors in a technologically advanced "scramble suit" that hides his physical features. The stress of his dual existence and his exposure to narcotics steadily fracture his sense of reality, causing him to separate his undercover identity from his law enforcement persona.

A small-time dealer of Substance D who operates cautiously in the Southern California drug scene. She serves as Arctor's primary drug connection and the subject of his deep romantic affection. Independent and highly guarded, she maintains strict boundaries regarding physical intimacy, keeping her relationships either purely transactional or emotionally distant.

One of Arctor's roommates, Barris is a highly educated and technologically savvy drug user. His room is littered with electronic components, reflecting his constant tinkering and scheming. He projects a helpful demeanor but frequently exhibits suspicious behavior, such as tinkering with Arctor's car and examining his broken cephalochromoscope.

Arctor's other roommate, a muscular man who participates heavily in the household's constant drug use. He tends to avoid the intense arguments that flare up between the others, preferring to coast through his high. He enjoys using drugs as an opportunity to theorize about life, though his focus is easily derailed.

Arctor's supervisor at the narcotics agency. He interacts with his undercover agents while wearing a scramble suit to conceal his identity, enforcing strict anonymity within the department. He manages the surveillance operations and focuses heavily on tracking down the high-level distributors of Substance D.

A heavy user of Substance D who constantly scrambles to secure his next supply of the drug. Highly anxious and already showing signs of early withdrawal, he lives in fear of a sudden drug shortage. He spends his days traversing the local streets and strip malls to avoid the physical agony of sobering up.

A routine user of the mind-altering Substance D whose intense drug consumption triggers severe neurological damage. He suffers from a permanent state of psychosis, entirely convinced his home is overrun by invisible aphids spread by human hosts.

A desperate drug user described as a needle freak. She agrees to have sex with Arctor in exchange for hits of a narcotic, illustrating the harsh, transactional reality of the doper community.

A woman struggling with addiction who lives with an abusive boyfriend and drug dealer. When her boyfriend violently slashes her tires, she refuses Arctor's suggestions to find a safer place to live.