In the world of literature for adolescents -- "young adults" as the publishers call them -- fantasy stories have a particular power to inspire loyalty. Think of J.R.R. Tolkien's sagas of Middle Earth, Ursula K. LeGuin's Earthsea books, Lloyd Alexander's Chronicles of Prydain, Madeleine L'Engle's Time Quartet, and all the rest.

These writers' ability to construct what Tolkien called "secondary worlds" -- complex environments sufficiently like our own to be recognizable but sufficiently different to generate excitement and wonder -- is the chief means by which they secure their readers' devotion. And it is precisely for this reason that something consequential is at stake when judging books of this kind: They offer not just a story but a world, and the lesson they teach is not just a moral but a worldview.

With the publication last week of The Amber Spyglass, the English writer Philip Pullman concludes the series that began in 1996 with The Golden Compass (or Northern Lights, as it was more appropriately called in England) and continued in 1998 with The Subtle Knife.

The collective title of the trilogy is His Dark Materials, and it clearly marks Pullman as a masterful maker of secondary worlds -- a writer whose talent puts him in the league of Tolkien, LeGuin, and Alexander.

Pullman's career as a writer, though distinguished, did not promise this. His children's mysteries set in Victorian London (the Sally Lockhart series) and his comic adventures (I Was a Rat!, Count Karlstein) are admirable, but none approaches the

In all other respects, His Dark Materials seems to come out of nowhere -- but readers and critics alike have already recognized Pullman's achievement. Even before The Amber Spyglass's release, it was twelfth on Amazon.com's bestseller list. The Golden Compass and The Subtle Knife, the previous books in the series, have reaped almost every award available and won places on the "best of the year" lists from Publishers Weekly, Booklist, and the American Library Association.

Remarkably, many successful fantasies are theologically freighted, and Pullman's is no exception -- but the theological freight his books carry turns out to be a distinct anti-theology. The phrase "his dark materials" comes from John Milton's Paradise Lost, and early in The Golden Compass the reader can already see that Pullman is retelling Milton's epic and, by extension, the Biblical narrative on which it is based. In His Dark Materials Pullman offers a Creation story with the familiar roles reversed: If, as William Blake said, "Milton was of the Devil's Party without knowing it," Pullman knows perfectly well whose side he is on.

Whichever party readers support in the ancient contest between God and Satan, they will be disappointed to see how often, in The Amber Spyglass, the tale's momentum is interrupted by polemic. Pullman's anti-theistic scolding consorts poorly with his prodigious skills as a storyteller. In imagination and narrative drive, he has few peers among current novelists. For such gifts to be thrust into the service of a reductive and contemptuous ideology is very nearly a tragedy.