The true subject of the book is to look at what happens to a small town that is suddenly and totally isolated. The first, urgent problem is a water supply. Pat Frank devotes some time to how serious this would be. He then cheats just a little. The town is located on a river.
People have to boil the water, but at least it exists and they can catch fish from the river.
Fish soon become the mainstay of the diet along with oranges. Because this is small, rural town many people have fruit trees. It is not a farming community, but still, a few people had gardens. In a nicely ironic touch, the people best suited to survive are the very poorest, the ones who, in their poverty, still kept chickens or pigs. One old man is the envy of the neighborhood.