This is another one of those books in the SF Masterworks series that I wouldn't really call SF attall. OK, it was set in the future but not by much. 1992 and the book was published in 1977. Just far enough to allow for a few minor differences, like the prevelence of a new and dangerous drug: Substance D.
John Arcter (codenamed "Fred") is an undercover narcotics agent and must live the life of a doper in an attempt to work his way up the chain of supply to try and find the ultimate source of Substance D. Things start to go awry however as the drug begins to damage his brain and his undercover persona becomes a suspect whom he must observe and report upon. His confusion grows as he begins no longer to recognise himself on the camera.
This book is a profiles drug abuse and the devestating effects that often result and the price they have to pay for their pleasures. It is more serious than other books I have read by Dick but it is not without humour. And unlike his other books, it doesn't attempt to mess with the reader's sense of reality, only that of the main character.
It's not SF, but it is a must