In his Hugo-award winning novel Spin (2005), Robert Charles Wilson managed to deploy a full panoply of both mimetic and speculative narrative tools and conceits. In a single novel he harnessed, side-by-side, the cosmic and the quotidian, creating a superlative example of literary SF, that often-idealized but intermittently achieved fusion that satisfies both genre fans and highbrow critics.

In his new book, Axis-the first of two planned sequels to Spin, and hence that innately awkward creature known as “the middle book of a trilogy”-Wilson veers much more heavily toward pure science fiction. It’s not that he neglects the virtues and charms of psychological realism. Far from it, since his characterizations and his observations about eternal human verities remain luminous, as does his prose. But by the very nature of the new book’s different venue and the futuristic events underway, the focus shifts away from a certain comfort zone beloved by readers of mainstream fiction. The result is a novel that feels like both a logical and valid extension of Spin, but also a lateral jump deeper into genre waters.

Perhaps we need first to remember what made Spin such a successful hybrid.

Launching from a more-or-less contemporary milieu, the book recounts what happens in the next few decades following a major anomaly in Earth’s history. One day our planet is simply cut off from the rest of the universe, trapped in a force bubble where time has slowed in relation to what’s happening outside. (Eventually the exterior universe will age by four billion years!) Three main protagonists — Jason and Diane Lawton and Tyler Dupree-go from adolescence to adulthood under this strange new regime, and we experience their emotional and psychological travails with as much interest and force as we do their attempts to unravel the cosmic conundrum.

In effect, Wilson wrote a novel of life during wartime, a whole planet under siege, the captive population’s stresses and triumphs. By blending this familiar and well-loved category of fiction with an alien threat, he captured the fancy of both those readers who relished an old-fashioned tale of sacrifice and endurance and love under conditions of privation, and those who liked weirdness and cognitive estrangement.

But Spin concluded with a twofold outward-bound release: human-derived Martian cousins arrived on Earth bearing a longevity formula; and the Hypotheticals, those never-seen aliens responsible for our predicament, opened up the Arch, a gigantic stargate leading to a hospitable new unpopulated planet.

Axis occurs some thirty years after this explicit invitation for mankind to venture forth into the unknown. The frontier planet called simply New World hosts scattered polyglot settlements and a flourishing economy. (The way various ethnic groups have capriciously mingled raises an echo of Michael Bishop’s prize-winner “The Quickening” , where alien intervention resulted in a similar blending.) Travel and commerce between Earth and New World is unrestricted. A Golden Age appears to have dawned, with the only hovering Sword of Damocles being the unknown intentions and nature of the Hypotheticals.

But one mixed group of Martian and human “Fourths” (those who have undergone the longevity treatment) is determined to remove even this last uncertainty, by establishing contact with the Hypotheticals. To do so, they have genetically engineered an embryo to function as the “communicant,” a living receiver who can tap into interstellar Hypothetical chatter. That embryo is now a twelve-year-old boy named Isaac, living in hiding and being sought by the agents of Department of Genomic Security.

Our heroine, Lise Adams, will find her fate becoming entwined with Isaac’s in dangerous fashion. With the help of rough-and-tumble bush pilot Turk Findley, her sometimes-lover, Lise is searching for her vanished father, Professor Robert Adams. Their sleuthing leads directly to Isaac and the outlaw Fourths. Bad enough-but danger is compounded for Lise and all humanity by a strange “rain” of living Hypothetical fragments!

Wilson establishes his backstory elegantly and unobtrusively, making this novel almost a beckoning standalone for newcomers. Yet the destiny of characters from the first book becomes integral to the new story. And with the fully fleshed-out Lise and Turk, Wilson has created a realistic romantic pairing of feisty individuals. Lise’s ex-husband, Brian, who happens to work for Genomic Security, is portrayed as a genuinely conflicted individual who eventually comes down on the side of the angels. Isaac, as reluctant demiurge, is firmly in the lineage of Wilmar Shiras’s Children of the Atom (1953) and John Wyndham’s The Midwich Cuckoos(1957). Alternating points-of-view allow the reader to inhabit all these folks from the inside.

Nor is New World itself left strictly to the imagination. Here, Wilson shows himself to be the heir to the pastoralism of Clifford Simak, as he lovingly evokes the flora and fauna of this new habitat, and the psychological effects the foreign ecology has on humanity. But Simak’s homely worldview always expanded under pressure to encompass and accommodate cosmic vistas in sane and undramatic ways, and here too Wilson echoes the master. Sentences such as this-” had enclosed the Earth in a strange temporal barrier, so that a million years might pass while a man walked his dog or a woman brushed her hair.”-might have flowed intact from Simak’s own pen. In fact, Wilson’s whole scenario calls to mind one of Simak’s most famous stories, “The Big Front Yard” (1958).

Wilson uses the word “labyrinth” consistently in this book to describe the fix mankind finds itself in. Lise’s Dad asks, “Is the New World a gift or is it a trap?” Wilson maintains a multivalent suspense about the motives of the Hypotheticals and the fate of humanity, and the novel fosters a deep sense of both moral and ontological perplexity. He seems to be leading to a scenario somewhat reminiscent of Gregory Benford’s Galactic Center Saga (six books from 1976 to 1995), where people occupied a precarious interstitial existence among older, more powerful and capricious races.

But as mentioned earlier, all this sorting-out of humanity’s new place in the grand scheme of sentience comes at a diminishment of the hearthside comforts and melodrama of the earlier book. Human emotions, even Lise’s deeply tested love for Turk, are bound to dwindle a bit in import and impact against such a backdrop. That’s just the inevitable price one pays for exchanging one’s mortal vision for the eyes of the Hypothetical godlings.