Because science fiction takes science seriously and because science takes the laws of nature seriously, the s.f. writer cannot simply let his imagination run free when he creates characters, setting and plot; he must always appear to be following some rules—even if he has to make them up himself. No one knows this better than Frank Herbert, whose favorite theme, appropriately enough, is the nature of godhood and what happens to men who reach for it.

[In "God Emperor of Dune"], the fourth but not necessarily the last in his best-selling Dune series, Mr. Herbert reshuffles all the elements of the fictional universe that he created in previous volumes. I cannot imagine anyone making sense of the story without having read the first three books. At times, Mr. Herbert's energy flags; and, behind the understandable world-weariness of his 3,000-year-old hero, we sense the weariness of an...