The book returns to the posthuman milieu Zebrowski mapped in his classic 1979 Macrolife. After an accidental chain-reaction renders Earth uninhabitable, the remnants of humanity retreat to scattered colonies and huge interstellar space stations called "mobiles," where nanotechnology bestows both near-immortality and practical utopia.

In itself, this setting offers Zebrowski a loom of cosmic scope on which to weave questions of potentially endless philosophical complexity. Macrolife is justifiably revered as one of the great SF classics, considered a "worthy successor to Olaf Stapledon's Star Maker" by no less than Arthur C. Clarke.

However, Cave of Stars falls short, both as a novel and as a work of ideas, because Zebrowski has stacked his literary deck and, in so doing, betrayed a lack of both charity and philosophical impartiality.

The central conflict of the book is nominally the encounter between a mobile and Tau Ceti IV, a planet-bound colony of Catholic refugees from Earth ruled by a pope. In reality, the plot serves as a vehicle for the author's natural anti-religious sympathies. In the presumably neutral narrative voice, Zebrowski refers to Tau Ceti as "shamefully backward," while "religious imagination" is "nothing more than a denial of the simple fact of decay." Theology is a "façade" that creates only "fear and self-loathing."

It is by no means necessary for a writer to acknowledge the existence of God to make a great book. However, a novel written under the weight of bias -- any bias -- loses the power shared by the best literary work, becoming at best an entertaining soapbox and at worst a grim polemic. Zebrowski aims higher than the entertaining soapbox, and so Cave of Stars must be judged on those lofty terms.

If a novel is a thought experiment, an inquiry into the causes and effects of human nature, then introducing pre-existing bias into the experiment sabotages the results and renders any conclusions suspect. The book and all of its characters are all either bewildered or disgusted by Tau Ceti's form of Catholicism, which apparently differs little from the form practiced on Earth today.

Surprising in a writer who earlier devoted a trilogy to the work of Catholic writer Teilhard de Chardin, Zebrowski has left no balancing factor, no room for argument. I expected a good science fiction novel with philosophical overtones; instead, I was left feeling betrayed after being beaten over the head with a single point of view for 270 pages.

Zebrowski also betrays his characters, manipulating them as though they were clay -- or, to use a somewhat pointed metaphor, like a stern God toying with creation -- in order to suit his chosen message. The pope of Tau Ceti, one of the most self-centered of the book's curiously small number of delineated characters, is portrayed as being alternately a rigid fundamentalist, capable of killing millions in the name of God, and a self-confessed apostate, gaining and losing his faith as the plot commands.

Other characters also suffer from this arbitrariness, moving about, falling in and out of love with a capricious abruptness, mouthing long speeches about the folly of faith and the obvious disparity between the enlightened utopia of the mobiles and the sour wretchedness of planet-bound and dogma-bound life. It is difficult to identify with such ciphers and, even more importantly, bewildering for the reader who even tries to make sense of their abstract changes of motivation and allegiance.

Other readers might find such reversals of character "complex," but I was hard-pressed to find much evidence that these changes were motivated by sincere personal evolution and not the dictates of Zebrowski's moral lesson.

As a result, it was difficult to care about any of the characters, who are painted without humor and whose virtues are told to the reader rather than shown in a way to encourage spontaneous emotional identification. All we are left with are their vices, which tend to center around either religious intolerance, smug self-satisfaction or both. I, at least, didn't care about what happened to them, but simply turned the pages in the hope they would stop talking about how bad it is to live on a theocentric planet in time for me to write this review.

As if this all weren't enough, Cave of Stars was slow going, and many of the scattered plot points hinged on the deus ex machina of accident -- a faster-than-light jump drive repeatedly fails, only to function correctly when the plot requires it, without explanation.

In a genre which has given us several classic works that have managed to combine both Catholicism and science -- Blish's Case of Conscience, Miller's Canticle for Leibowitz -- Cave of Stars left me disappointed. Had Zebrowski allowed his characters the free will to speak their own minds and make their own choices, for good or for evil, he might have produced a book that transcended Macrolife in its relentless search for the heart of human existence.

(Harper Prism, 273 pp., September 1999)