Riddley Walker is set about two thousand years after a nuclear war has devastated world civilizations. The main action of the story begins when the young narrator, Riddley, stumbles upon efforts to recreate a weapon of the ancient world.
The novel's characters live a harsh life in a small area which is presently the English county of Kent, and know nothing of the world outside of "Inland" (England). Their level of civilization is similar to England's prehistoric Iron Age, although they do not produce their own iron but salvage it from ancient machinery. Church and state have combined into one secretive institution, whose mythology, based on misinterpreted stories of the war and an old Catholic saint (Eustace), is enacted in puppet shows.