One of the most bewildering of PKD's already bewildering collection of novels, and yet one of the most powerful. This one doesn't reach as far into the future as most of his novels, there are none of the usual precogs, martian colonies and androids that are the author's hallmarks. Rather we only jump a few fictional years ahead to a future where Substance D, a narcotic in a league above all current ones available.
As last time - I'll post up a more concise summary than I'm able to conjure from a summary of the series at SFSite.com
"It follows the story of Officer Fred, an undercover narcotics agent who is so deeply undercover that even his superiors don't know his street identity, Bob Arctor. Consequently, Fred is given the task of monitoring Bob.
The problem is, Fred/Bob isn't sure which side he is on anymore, since he more than half believes in the drug culture lifestyle he has been living. Furthermore, he is so messed up on a dangerous psychotropic hallucinogen called Substance D, that he is losing touch with... well, everything. The literal scanner of the title (seeing "through a scanner darkly") is a holographic scanner set up in Bob's house. When Fred watches the replay of the scanner tapes, he is soon unable to figure out what Bob is up to, having forgotten he is monitoring himself."This book has the most impact as it relates most closely to the author's life and the impact of drug abuse on him and his friends. It ends with a moving piece from the author detailing how they were like kids playing in the road, and no one told them about the danger, following this is a list of many of his friends from that time who are sick, in institutions or lost along the way.
Not always the most exciting read, but certainly one of the most moving.