Simulacron 3 is the story of a virtual city (total environment simulator) for marketing research, developed by a scientist to reduce the need for opinion polls. The computer-generated city simulation is so well-programmed, that, although the inhabitants have their own consciousness, they are unaware, except for one, that they are only electronic impulses in a computer.
The simulator's lead scientist, Hannon Fuller, dies mysteriously, and a co-worker, Morton Lynch, vanishes. The protagonist, Douglas Hall, is with Lynch when he vanishes, and Hall subsequently struggles to suppress his inchoate madness. As time and events unwind, he progressively grasps that his own world likely is not "real" and might be only a computer-generated simulation.