Spin was not merely good, but extraordinary. So it would be unfair to label its sequel Axis a disappointment. What it lacks are the layers of thematic complexity that made Spin both an intellectually and emotionally transcendent achievement. But though it comes directly from its author's comfort zone, Axis is a worthy extension of Robert Charles Wilson's Hugo-winning original, introducing new elements of mystery to the inscrutable alien Hypotheticals, and offering just enough action and heart to offset the use of some stock characters and rather obvious religious allegory.
Spin ended with the opening of a tremendous Arch in the Indian Ocean linking the Earth to a new world, Equatoria. This, we discover, is but one of a ring of linked planets amenable to human life. Why exactly the ineffable alien Hypotheticals chose to encase the Earth in a temporal coccoon that propelled us billions of years into the future in the first place remains shrouded in obscurity. Homo sapiens being who we are, many have projected profound motives of religious or spiritual transcendence upon it all. It's a measure of how deeply we want the universe to be about us, rather than simply accept that we just may be one more thing getting in its way now and then.
The Spin's impact upon the human race has, needless to say, been monumental. The passage of the eons saw the rise and fall of human civilizations on Mars, where a life-extension procedure derived from Hypothetical science has long been illegal on Earth, and those who have augmented themselves with it — the Fourths — are shunned. Many Fourths now have fled to Equatoria, where they are no less mistrusted. (The procedure adds about 20-30 years to human life expectancy, with the caveat that you will become a bit less emotional, a bit more even-tempered and rational. It does not sound to me like all that devastating a trade-off.)
The mistrust, we quickly find, is earned. The Fourths have been trying to breed what you might call — tell me you've read Dune so I don't have to recap it for you — their own Kwisatz Haderach, a child modified in the womb who will, it is hoped, be able to communicate directly with the Hypotheticals. It takes a true fanatic to want to speak face to face with his God. It also takes forgetting the old adage about the wisdom of meeting your heroes. In any case, the possibility that such a child has been born on Equatoria will bring several players together. Some of them, like the desperately devout Fourth scientist Avram Dvali, pursue revelations with little thought to consequences. Their adventure will coincide with the arrival of dust storms, made up of not just any dust, that blanket Equatoria and open up a whole new set of questions about the Hypotheticals.
Wilson is a rare bird in hard SF circles in that the wealth of imagination behind his ideas is always on an equal footing with his sensitivity to character. The players here are a fine and diverse bunch — Turk Findley, a young pilot escaping a dark past on Earth; Lise Adams, seeking the fate of her father, who vanished in his own pursuit of rumors of a special child; Sulean Moi, the Martian Fourth who has seen first-hand the horrific effects of this breeding experiment and desperate to prevent further tragedy.
But if Axis has a central fault, it is that it feels like so many middle novels in trilogies feel: a bridge between far superior first and final volumes. The story eventually settles into a long chase, never as suspenseful as it could be because the pursuers — including Lise's estranged husband and a couple of Mutt-and-Jeff special agent stereotypes — have too little narrative presence. The climax itself is, I gotta say, quite the bravura setpiece. But while it allows some of the characters, like Findley, to resolve their arcs in a satisfying way, Axis still leaves you with less of a sense of wonder for its own storytelling accomplishments than with a sense of "To be continued..."