James Herbert's novel The Fog (1975) doesn't have quite as much nudity and sex in it as the totally awesome cover might suggest, although there is certainly as much sex (and some of it rather disturbing) as you would expect any self-respecting 1970s horror novel to contain.
John Holman is an investigator for the Department of the Environment who is driving back to London from a secret stakeout at a military installation in rural Britain. As he enters a small town, the ground starts shaking, the highway splits apart and his car falls into the crevasse in the earth. He manages to get out of his car and crawl towards safety, but on his way out he is surrounded by a strange yellow fog escaping from deep in the earth. When the rescuers finally pull him from the ground, he is completely violent and insane.
Holman is restrained in a hospital, gets a blood transfusion, and fights his demons for several days before returning to his regular self. His girlfriend stands by him, and the two of them begin the drive back to London. But as they drive, they run into the mysterious yellow fog -- and it is getting bigger.
This book was really well written and entertaining -- it ultimately moves between Holman who has to convince the government that the fog is dangerous, and who is quickly recognized as the only person who is immune to the effects of the fog, and a series of vignettes of the different people who come into contact with the fog with horrible results. This novel is part government conspiracy, part zombie attack, part creepy isolation, and a whole lot of yellowish fog that becomes a character in its own right.
The characterization of big and small players in the book is excellent -- sometimes funny, sometimes disturbing, and always effective. Some of the description is so cinematic that I can't believe no one has made this into a movie: the entire population of a seaside resort walking into the ocean; spotting all the pigeons of Trafalgar square sitting motionless in the fog and ready to attack at a moment's notice; opening the curtains after some "everything is finally okay" sex to nothing but blank yellowish fog... (Note: John Carpenter's wonderful movie The Fog (1980) is not related to this book.)
I haven't read a straight-up horror novel for many years, and The Fog made me want to revisit some of my favorites...
[Thanks to the lovely Dan for letting me steal this out of his garage sale pile...]