A small town in rural Pennsylvania is imprisoned behind an alien force-field "wall" at the very instant of worldwide nuclear war. At first, the terrified and bewildered residents did not know what to expect of their alien jailers--Had the aliens started the holocaust? Was the town to supply human subjects for alien experimentation?--but soon the rigors and emergencies of survival blotted out all other concerns. Beyond the transparent Wall the Earth was dying as clouds of radioactive dust obscured the sun. Within the Wall, the townspeople gradually relearned the skills of primitive societies: milling corn, weaving cloth and sharing burdens. It is Isabelle, one of the first children born after the holocaust to survive to maturity, who begins to question the passive attitude of the townspeople toward their extraterrestrial enemies, and who precipitates a conflict that leads to unforeseen hope.