The story is set about two years after the collapse of civilization due to a mysterious disease called neuroderm.
The "disease" is actually caused by a symbiotic micro-organism sent to Earth from another inhabited planet, and is actually beneficial, though seen as disfiguring because of the graying of skin which eventually spreads over the entire body.
Paul discovers that Houston is now controlled by a strongman named Georgelle, whose followers exterminate any "dermies" they come across.
Paul finds that Galveston Island is an all-dermie colony which had deliberately destroyed all bridges leading from the mainland.
Eventually, Paul overcomes his fears about neuroderm for the sake of Willie, and plans to go with her to some small island until sanity returns to the world.