Lewis’s science-fiction trilogy is sometimes called the Ransom Trilogy, after the central figure of Out of the Silent Planet and Perelandra. Elwin Ransom, a middle-aged linguistics professor at the University of Cambridge, grows in the course of the novels from a lonely independence to find relationships with others, maturing into a leader against hostile nonhuman forces. Lewis transforms a conventional science-fiction pattern by making his villains demoniac powers and his protagonists Christians literally on the side of the angels. While science fiction has frequently dealt with issues of religion, Lewis lays aside the typical dualistic “good against evil” plot for an explicitly Christian worldview. All three of the novels attempt to make believable the presence of a spiritual reality transcending the everyday life.

Out of the Silent Planet opens as Ransom, on a walking tour of England, falls in with two acquaintances, one an old friend from his prep school. His friend Devine and the scientist Weston kidnap Ransom, carrying him to Mars, or Malacandra, in Weston’s spaceship. Late in the voyage, Ransom learns that the others were commanded to bring another human back as the condition of their return. When they land, Ransom escapes. The novel is so far entirely conventional: mad scientist, greedy assistant, innocent victim, threatening aliens.

Here, however, Lewis diverges from convention. Ransom finds Mars inhabited by three species of rational beings, all friendly. More, he finds present a fourth species, the eldila, something on the order of angels. After Ransom learns the Martian language, he is reunited with Weston and Devine, who have killed a Martian. Judged by the ruling eldil, the Oyarsa, all three are exiled to Earth. Ransom learns from the Oyarsa that Earth is the “Silent Planet” because of the rebellion of its Oyarsa millennia ago. It becomes clear to Ransom, already a Christian, that the biblical story of the incarnation of God in Christ is historically true, one incident in a war that has left Earth isolated and dominated by evil powers.

Two elements of the story are particularly significant: first, the minimal place of “science” in the action, and second, the “reperceptions” that Ransom experiences. The “good society” of the Martians is almost Rousseauian in its rejection of technology, and the one species with which Ransom spends much time is a tribe of hunters and farmers. Ransom must repeatedly adjust his perception of the landscape, his understanding of culture, and his sense of what it is to be “human.” He discovers a new sense of his own place and that of humanity in a universe of many intelligent species and a new humility, in that humankind is the sole species in need of redemption.

In Perelandra, Ransom is summoned to Venus to defend its inhabitants from an unknown threat. He discovers that only two “humans” have been created, the Adam and Eve of their race. Like Adam and Eve, they have a single commandment given them, which they must obey to show their love for God. Weston’s sudden arrival in a new spaceship makes clear the nature of the threat. Proclaiming himself the servant of the demoniac Oyarsa of Earth, Weston begins a campaign of temptation against the unfallen Eve, the Queen.

Lewis’s study of John Milton’s Paradise Lost (1667, 1674) lies behind many of the novel’s scenes; the temptation, for example, recapitulates Milton, not the Bible. Like Milton, Lewis faced the problem of portraying “goodness,” unfallenness, in the Queen. The difficulty of successful characterization is enormous: She is simultaneously innocent, gracious, wise, and naked. At the same time, Lewis must portray the decaying personality of Weston as suggesting...