The novel follows the struggles of engineer John Custance and his friend, civil servant Roger Buckley, as, along with their families, they make their way across an England which is rapidly descending into anarchy, hoping to reach the safety of John's brother's potato farm in an isolated Westmorland valley. Buckley, having advance warning of the government's plot to hydrogen bomb major cities, alerts Custance to evacuate. Picking up a travelling companion in a gun shop owner named Pirrie after an attempt to procure arms, they find they must sacrifice many of their morals in order to stay alive. At one point, when their food supply runs out, they kill a family to take their bread. The protagonist justifies this with the belief that "it was them or us."