It seems like there’s been an uptick in parallel world tales of late. Perhaps outer space holds less appeal as a new frontier for science fiction; alternate earths, instead, are where the greener fields lie—sometimes literally. Neal Stephenson has produced his own riff on the many-worlds theory in Anathem, and Iain M. Banks’s Transition features a secret organization of “transitionaries,” who slip from one world to the next by temporarily taking over the bodies of inhabitants of each world. Matt Fraction’s comic Casanova is about an assassin yanked out of his own timeline to replace his own alternate self in another as part of a complex, worlds-spanning espionage scheme. Even Doctor Who has played extensively with parallel worlds and alternate timelines. The latest addition to the genre: The Long Earth, a collaboration between Terry Pratchett and Stephen Baxter.

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In The Long Earth, the multiverse is conceived as a series of parallel timelines, all a short quantum step away from one another—most of which contain absolutely no human beings at all. Throughout history, a scant few humans from our Earth—Datum Earth, as it’s called—have been able to access the other Earths through a natural talent for “stepping,” but since the events of Step Day, when millions of children the world over activated their “stepper boxes” (instructions suddenly and anonymously distributed all over the internet, easy to build with parts found at any Radio Shack, and powered by a potato), almost anyone can do it. You can only bring what you carry, not including anything made of iron or steel, and unless you’re one of the rare folk who can step naturally, you’ll get violently ill for a few minutes after. But the new worlds are pristine and undeveloped, ripe for exploration—and if you’re not one of the unlucky folk who are simply unable to step at all, the Long Earth offers a new frontier, a new place to start over.

Joshua Valienté is a natural stepper with the unique distinction of having been born on another Earth—his young mother stepped there just long enough to give birth. Since Step Day, he’s been the Daniel Boone of the Long Earth, acting as a guide to the newcomers who are busily colonizing the parallel worlds. He is hired by the driving force behind the transEarth Institute, a whimsically-minded AI that calls itself Lobsang, for an exploratory mission to see just how far the Long Earth goes. Step far enough and you’ll find a world where the ice age hasn’t ended, or one where the entire planet is covered with ocean and enormous things with very big teeth swim in the depths.

More importantly, though, there are other sentient creatures that can step through the Long Earth. There’s what Joshua and Lobsang call the “trolls,” monkey-like, bear-like bipeds that are generally peaceful, and which communicate through song. And there are also the “elves,” a nastier biped species that uses its stepping ability to become deadly hunters. And there’s something else out there—something that’s causing the trolls and the elves to flee across the Long Earth, and Joshua is destined to find it.

Meanwhile, Earth’s population is slowly being siphoned off across the new worlds, as those with the means and desire to do so strike off to find new homesteads. Governments and law enforcement scramble to determine jurisdiction—do the police in the Madison, WI of Datum Earth still have the ability to arrest someone in the Madison-equivalent of an Earth ten steps over? National economies are in trouble as the work forces are drained away, and criminals have figured out how to exploit stepping for break-ins or worse. And the segment of humanity that is completely unable to step—”phobics,” in the less kind parlance of the time—are resentful and angry, perfect fuel for a demagogue in the right place at the right time.

It’s a lot of ideas, themes, and characters for one book to carry, and it’s impressive that Pratchett and Baxter carry it off so gracefully. The cast of characters is enormous—in addition to Joshua and Lobsang, there’s Monica Jansson, the police officer who has been keeping an eye on Joshua since Step Day; the Greens, a middle-class American pioneer family hauling “out West” to a far-flung Earth to start over (even though it means leaving the “phobic” son behind); Sally Linsay, another natural stepper; and many more men and women touched by the changes wrought by the discovery of the Long Earth.

As you’d expect from these authors, the writing is elegant and witty, peppered with sly pop-culture references. The worlds of the Long Earth are all richly rendered, and even the walk-on characters are deftly imagined. Ironically, if any portion of it doesn’t completely succeed, it’s Joshua and Lobsang’s rambling journey, during which the reader may become as frustrated as Joshua does with Lobsang’s habit of witholding information to drive the quest (and thus the plot) forward. The conclusion feels slightly rushed and not entirely satisfying; the great reveal at the end of their journey is a little too easily resolved, the questions raised about the nature of sentience and human intelligence talked through a little too quickly.

Of course, it’s worth remembering that this is the first part of a series; many issues arise quite late in the book that clearly need another volume or three to fully explore. And the final scenes on Datum Earth leave the reader with a wrenching cliffhanger. Minor flaws notwithstanding, The Long Earth is a genuinely thoughtful and entertaining exploration of a profoundly changed universe—and the potential seems endless not just for the characters, but for Pratchett and Baxter as well.

Karin Kross lives and writes in Austin, TX. She can be found elsewhere on Datum Earth on Tumblr and Twitter.