The film tells the story of an expedition led by a figure known as the "Stalker", who takes his two clients—a melancholic writer seeking inspiration, and a professor seeking scientific discovery—to a mysterious restricted site known simply as the "Zone", where there supposedly exists a room which grants a person's innermost desires. The trio travel through unnerving areas filled with the debris of modern society while engaging in many arguments.

References:
https://en.wikipedia.org/wiki/Stalker_(1979_film)