"A Scanner Darkly" is a science fiction novel by Philip K. Dick, published in 1977. The story is set in a dystopian future where a powerful drug called Substance D causes severe psychological effects. The protagonist, Bob Arctor, is an undercover agent who becomes addicted to the drug while trying to infiltrate a group of users. The narrative explores themes of identity, surveillance, and the impact of drug addiction. As Arctor's dual life unfolds, he struggles with his sense of self and the consequences of his actions. The novel raises questions about reality and the nature of consciousness in a society plagued by paranoia.