EXPIRATION DATE, <i> By Tim Powers...

Some writers essay again and again the same virtual territory, circling ever more tightly inward toward fundamental themes, preoccupations and apperceptions, striving to get it, finally, absolutely, right. Others palpably change and develop with each novel, taking on new subject matter, extending their reach, pressing the scope of their regard and ambition. A few, a scant handful, do both.

Tim Powers, for instance.

The writer he most reminds me of in his best moments is Theodore Sturgeon. Powers is not the stylist Sturgeon was, of course, but he’s every bit the storyteller. And I can’t imagine a higher recommendation.

Beginning with novels such as “The Anubis Gates” and “Dinner at Deviant’s Palace,” clicking into place forcibly with “The Stress of Her Regard” and 1994’s “Last Call,” Powers has forged a style of narrative uniquely his own, one filled with sharply drawn characters, fully imagined settings, elaborate underpinnings that pull all rugs out from under us and let us glimpse terrible, ragged floors beneath.

The purport of Powers’ fantasy (perhaps of all serious fantasy) is ontological: To insist that things are not as they seem, that what we perceive as the world about us is but a scrim over something really quite different and ultimately unknowable.

His plots begin when, for one or another of his characters, a tear appears in the veil.

In Expiration Date (Tor: $23.95; 381 pp.), that character is 11-year-old Koot Parganas, who breaks into his parents’ plaster bust of Dante and inhales the long-hoarded ghost of Thomas Alva Edison. Soon Koot and Tom are a team and most of the book’s other characters are after them: Nicky Bradfield, onetime child TV star who, though dead, remains in the world through sheer force of will, subsisting wholly on cinnamon candy and setting out stuffed pigs that hoot at the approach of other ghosts; Sherman Oaks, a one-armed ghost hunter who uses his phantom limb as a kind of dowsing rod; Pete Sullivan, who hopes to rescue his dead father from ghost-devourer/filmmaker Loretta DeLarava.

Add to all that the death mask and severed thumb of Houdini, some monstrous rotting thing crawling from the sea and an inner city filled with ghosts who, speaking gibberish, consuming rocks and bottle caps, have accumulated just enough physical substance--from bugs and sick animals, from spilled blood and spit and semen--to lurch about panhandling, and you’ve a fair idea of the landscape here.

Set in a present-day Los Angeles that’s tumbled down the rabbit hole after Alice, “Expiration Date” is a fine melange of the fantastic and mundane, its outlandish loops and limbs and odd-shaped parts at last locking down, in purest Tim Powers fashion, into a richly textured, eminently human, whole.

Alternate history has established itself in recent years as a popular and progenitive tributary of speculative fiction, giving us such fine and diverse books as Jack Womack’s series, now in its fifth volume, and Michael Bishop’s elegiac novel starring Phil Dick. At the forefront of this trend, author of dozens of such stories and novels, in particular of a much-acclaimed alternate-history Civil War novel, “The Guns of the South,” is Harry Turtledove, a historian who, failing to find honest work, found his own alternative history as novelist.

And now as Richard Dreyfuss’ collaborator.

The Two Georges (Tor: $23.95; 384 pp.) is set in present-day North America--a North America, however, in which colonists never rose up against Britain and remain, as the North American Union (NAU), a part of the empire. The famous Gainesborough painting of His Majesty George III and George Washington that serves as the symbol of unity of the empire has been stolen, and held ransom, by an extremist group calling itself the Sons of Liberty. Royal American Mountie Thomas Bushell, there when the painting was taken and responsible for its safety, vows to recover it at any cost.

And so we follow Bushell from luxury dirigible rides to jaunts about New York in steam-powered cars, join his expeditions to the independent Indian nations and northwestward to the edge of Russian-held Alaska, sounding what the Rights of Man and Jeffersonian ideals have become in this America where Jefferson (and, indeed, Jackson) never arose, where Martin Luther King is governor-general of the NAU and “Common Sense” a conservative political rag.

The stew’s a tasty one, full of nourishment and substance. The stew well-spiced with humor, with marvelous touches of irony and satire, and with those “precise, telling details” of which Chekhov was so fond: Matches are lucifers, undershirts vests, a telephone exchange begins AGincourt.

Throughout, the novel is also a fine adventure story, wonderfully plotted and paced, replete with fully imagined characters, unusual settings, unexpected turns. It should appeal strongly to readers who in recent years have so embraced novels such as Caleb Carr’s “The Alienist” and Peter Hoeg’s “Smilla’s Sense of Snow.”

Orson Scott Card’s Pastwatch (St. Martin’s: $23.95; 351 pp.) is alternate history of a different sort--on a grander scale, certainly, and far more discursive: so discursive, in fact, that the book reads in parts like a tract, giving the whole a curious kind of coldness or distance that forestalls our connecting with the novel’s characters.

“Pastwatch” shares, with Tim Powers’ “Expiration Date” and with other Card novels such as “Ender’s Game,” its youthful hero and (with much of traditional science fiction) the questionable premise that one man, given enough intelligence and time, can change history’s course.

While the novel’s subtitle, “The Redemption of Christopher Columbus,” offers some notion of what this novel is about, it scarcely hints at the haystacks of material packed into this relatively short novel: elaborate theories of civilization; speculation as to religion’s influence on cultural and intellectual change; histories of Mayan, Toltec and Aztec culture; discussions of human sacrifice and slavery; intercut first-person narratives spanning Columbus’ life, both real and imagined. And if the book, as novel, founders under this cargo’s weight, nevertheless it remains a fascinating read.

In a physically exhausted future world, aided by new technologies allowing access to the past, people turn for solace and for whatever understanding might still be possible, to what remains most human and central to them--to their stories, their individual and collective histories, to the way generations have come into being, survived, adapted and failed to, died.

Because the world has so small a future, its past looms huge. And finally these people are nothing more than their past, their history. But if they could change that history. . . ?

What moment would they choose, what fulcrum point, to transform all mankind?

Focusing on the attempts of a small group of colonists first to conquer, then to avoid or control, finally to understand and embrace their new world’s environment, Beowulf’s Children is the most traditional of the novels under review. For many it will recall early delights of reading science fiction, how as young readers we sank to our shoulders in Heinlein, Asimov or in Niven’s “Ringworld,” our wonder at the headlong narrative, the pleasures of watching an unknown ecology or social system unfold before us, breathless, mysterious encounters with alien life forms, sagas of challenge, of human understanding and adaptability pushed to the very edge. Youthful protagonists. Heroism.

In this regard few writers have a finer pedigree than those here. Many of Niven’s novels are classics; such collaborations with Pournelle as “The Mote in God’s Eye” and “Lucifer’s Hammer” rank high among reader’s favorites: Steven Barnes has previously joined one or both in co-authoring “Dream Park,” “The Legacy of Heorot” and others.

And indeed, as one might suspect, “Beowulf’s Children” is seamless, its unfolding of the new home planet’s ecology and its high-adventure narrative skillfully interwoven, its several stories and themes painstakingly overlapped, the novel very much of a piece and tone.

Any such novel, of course, requires a heavy cargo of background, of inert exposition, as the reader is formally introduced to a new world. Here, I think, the novel’s form, its progression by accrual, with brief, ever-shifting scenes and viewpoint, amplifies the problem, so that initially readers may find getting purchase on the novel a bit difficult. On page 106, though, when one of the book’s monsters, Old Grendel, surfaces in her own voice, the book springs to life. From there on out, to the novel’s complex, redemptive conclusion 276 pages later, everything is good wind, high sea, safe passage, making “Beowulf’s Children” an absorbing, substantial and finally rather masterful novel.