“His Dark Materials” may be the first fantasy series founded upon the ideals of the Enlightenment rather than upon tribal and mythic yearnings for kings, gods, and supermen. Pullman’s heroes are explorers, cowboys, and physicists. The series offers an extended celebration of the marvels of science: discoveries and theories from the outer reaches of cosmology—about dark matter and the possible existence of multiple universes—are threaded into the story. Indeed, the central mystery of “His Dark Materials” concerns the nature of Dust, a dark matter-like substance that the scientists of Lyra’s world have only recently learned how to detect. Dust is everywhere, but it tends to concentrate around human beings, and around adults more than children. The Church considers Dust to be the “physical evidence for original sin.” Lyra’s father, a Byronic figure named Lord Asriel, defies Church prohibitions by mounting an expedition to the Arctic Circle, where he learns more about Dust by observing another universe, which can be glimpsed through the northern lights. Her mother, the treacherous Mrs. Coulter, is secretly running an isolated camp in the same region, where she conducts sinister Dustrelated experiments on abducted children, under the aegis of the General Oblation Board, one of the Church’s more malevolent offshoots. It is this outfit that kidnaps Lyra’s best friend, setting the story in motion.

What readers tend to find most alluring about “His Dark Materials,” however, is a wholly unscientific invention. Every character in Lyra’s world has a daemon—an animal-shaped alter ego that is all but inseparable from its human counterpart. Not that the relationship is always congenial. In the first scene in “The Golden Compass,” Lyra quarrels with her daemon, Pantalaimon, about breaking the college rules, much as characters in more conventional stories might argue with their consciences. The device could be gimmicky, but Pullman wields it with elegant metaphorical economy. Not only do daemons answer the writer’s need to turn a character’s internal struggles into drama; they speak to the ache of consciousness and the desire for an ideal companion. Children, owing to the plasticity of their personalities, have daemons that can change shape—in the opening scene, Pantalaimon transforms from a moth into an ermine—but as a person comes of age his daemon settles on a single form that reflects his essence. In Pullman’s version of the Fall of Man, the loss of a protean innocence leads to a gain in self-knowledge.

Pullman also makes the argument that Lewis really isn’t all that Christian. The fate of Susan Pevensie, he told me, indicates “some sort of crazed, deranged Manichaeism. Here’s a simple test: What is the greatest Christian virtue? Well, it’s charity, isn’t it? It’s love. If somebody who knew nothing about Christian doctrine, and who had been told that Lewis was a great Christian teacher, read all the way through those books, would he get that message? No.”

Sexual love, regarded with apprehension in Lewis’s fiction and largely ignored in Tolkien’s, saves the world in “His Dark Materials,” when Lyra’s coming of age and falling in love mystically bring about the mending of a perilous cosmological rift. “The idea of keeping childhood alive forever and ever and regretting the passage into adulthood—whether it’s a gentle, rose-tinged regret or a passionate, full-blooded hatred, as it is in Lewis—is simply wrong,” Pullman told me. As a child, Lyra is able to read a complicated divination device, called an alethiometer, with an instinctual ease. As she grows up, she becomes self-conscious and loses that grace, but she’s told that she can regain the skill with years of practice, and eventually become even better at it. “That’s a truer picture of what it’s like to be a human being,” Pullman said. “And a more hopeful one. . . . We are bound to grow up.”