Book excerpt: Twenty-six of the greatest science fiction stories ever written. Robert Heinlein in "The Roads Must Roll" describes an industrial civilization of the future caught up in the deadly flaws of its own complexity. "Country of the Kind," by Damon Knight, is a frightening portrayal of biological mutation. "Nightfall, " by Isaac Asimov, one of the greatest stories in the science fiction field, imagines a planet where the sun sets only once every millennium and is a chilling study in mass psychology.