The peaceful life of a village in Wiltshire is suddenly shattered by a disaster which strikes without reason or explanation, leaving behind it a trail of misery and horror. A yawning, bottomless crack spreads through the earth, out of which creeps a fog that resembles no other. Whatever it is, it must be controlled; for wherever it goes it leaves behind a trail of disaster as hideous as the tragedy that marked its entry into the world. The fog, quite simple, drives people insane.