A couple encounter mysterious atmospheric effects in an airplane and find themselves in a town where people behave oddly. They eventually escape.

Catherine, in her 9th month of pregnancy, begins to have labor pains while on vacation in the mountains. Her husband, Mark, charters a plane from Tony, a former Korean War pilot, in the hope of reaching a hospital before the baby is born. Forced to make an emergency landing when they become lost in a storm, they find themselves in a strange community whose residents move mechanically, as if under a hypnotic spell. A characteristically afflicted doctor from the community delivers Catherine's baby safely. Later, the visitors discover that the area is covered by a huge, transparent dome and that once a week a resident disappears, presumably to be studied by the aliens who have trapped the community in a "zoo." Mark and Catherine take refuge in an old mill in the countryside while Mark attempts to dig an escape tunnel under the dome. Mark and Tony discover a mysterious rock structure in which they find a seat. Tony receives a convulsive shock when he sits in the seat, and grotesque faces swirl around him. Permanently affected by the experience, Tony eventually disappears. Mark then destroys the seat in an attempt to enlist the aid of the doctor. The community's source of food is thereby discontinued, and the starving citizens eventually follow Mark and Catherine to their unfinished escape route.