One of the defining modes of science fiction is the space opera: that type of galaxy-spanning tale commonly apprehended by the general public under the Star Wars or Star Trek franchises. (Although in print there are many other more ingenious and more subtle examples, from Isaac Asimov to Frank Herbert, from Edmond Hamilton to Kevin J. Anderson.) In fact, so strong is the equation of “SF = space opera,” that for decades the whole genre was known to the undiscerning hoi polloi as “that Buck Rogers stuff,” after one of the earliest examples of the brand.

But having space opera as the beating heart of science fiction has always involved a contradiction. Much of the apparatus of space opera is deemed scientifically impossible, while SF at its best honors the strictures and principles of physics and other applicable disciplines.

The ability to travel faster than the speed of light — a necessary to maintain any self-respecting star empire — is currently deemed forbidden by today’s theorists. Psychic powers such as George Lucas’s “Force” have scant credence among today’s skeptical savants. And the complex sociopolitical systems that would be necessary to organize and rule hundreds of planets and trillions of species would in all likelihood not default to Emperors and Jedi Knights.

Seeking to draw space opera closer to reality and further away from fairytales of blood and thunder, certain writers have postulated future polities spread across multiple solar systems in a less florid and more realistic manner. Karl Schroeder (Lockstep) and Charles Stross (Neptune’s Brood) are two such authors who recently adopted this approach.

And then there are those scenarios that confine humanity to our one natal solar system, but which find future citizens ingeniously inhabiting every possible niche, however harsh, producing a galaxy’s worth of exoticism within a compact and feasible volume. While John Varley might be seen as the postmodern pioneer of this mode, with his Eight Worlds continuity, the roots actually extend back further, to the Planet Stories magazine oikumene of which Leigh Brackett — who later went on to pen The Empire Strikes Back — was a prime progenitor. In such a universe Mars was always ancient and dry, with immemorial vestiges of past glory; Venus was young and wet and populated with thunder lizards and intelligent frog creatures; and Jupiter’s vast gravity produced stocky supermen. A recent superlative example of this, updated to cutting-edge standards, was Kim Stanley Robinson’s 2312.

The two writers — Daniel Abraham and Ty Franck — today collaborating under the pen name of James S. A. Corey apply the label “space opera” to their series known as The Expanse.

In the first three Expanse books, the authors have produced a milieu that fosters the same kind of thrills found in the “widescreen baroque” form of space opera, but in a manner more palatable to readers concerned with accurate and believable futurism. Then, in Books 4 and 5, they do indeed move out into the early days of galaxy hopping. While they publicly decline to be known as “hard SF” writers, they invest their action with gritty naturalism.

Book 1, Leviathan Wakes, plunged us without preamble into a fully fleshed out future a couple of centuries from now, as tactile and coherent as any historical era. Earth, the mother world, is powerful but burdened by 30 billion inhabitants. Mars, the oldest colony, is likewise regnant, in a tentative union with Earth. The Asteroid Belt is full of roughshod miners, settlers, and dissidents (“Mormons in Space,” anyone?), as are many of the outer moons. These pioneers form the Outer Planet Alliance, or OPA. The various factions and communities of the buzzing solar system are webbed together with commerce in a flourishing setup that nonetheless features power struggles for any upper hand.

Having limned this arrangement, Corey quickly establishes the efficient and compelling narrative template for the series. And any writer who hopes to produce nearly 3,000 pages of a series (to date only, with the story unconcluded) is going to rely on a solid narrative structure reestablished with each new book.

First, each chapter will advance the story from the limited point of view of one of the protagonists. But our main hero in every book will be James Holden — former soldier, good-natured and altruistic but easy to anger. When we first encounter him, he’s a bit of an unmotivated space bum, killing time in a competent, utilitarian fashion.

Second, one major plot thread will power each novel and be resolved by the book’s end, but will thence open outward to the next installment.

And last, there will be myriad subplots, some of which prove more intrinsic than others.

This first adventure revolves around a missing woman, Julie Mao. An embittered and brutal Martian detective, Joe Miller, gets on her trail. Meanwhile, Holden and his three buddies, Alex, Amos, and Naomi, who will come to form the tightly bound crew of the salvaged warship Rocinante, have their boring water transport jobs literally shot out from under them, sending them down a path of investigation and revenge. The vectors of Miller and Holden & Company converge on the discovery of a 2 billion-year-old alien relic, the “protomolecule.” This active agent, prodded to life by greedy human intervention, has transformed Julie Mao and soon infects a whole settlement.

Readers will immediately note that Corey is a dab hand at constructing propulsive, elongated action scenes that move from cliffhanger to cliffhanger. Both scenes of combat and scenes of wrestling with the unforgiving vacuum of space compel pulse-pounding speed reading. The focus of the book on inhabiting various “steel beach” environments (to employ John Varley’s metonomy), in opposition to any conventional planetary surface, speaks to the transition humanity has really made, to living as a creature of deep space. And yet, aside from a little high-powered medical technology (mostly invoked to repair our incredibly banged-up heroes in timer for their next outing), our cast is not weirdly “posthuman,” as in, say, Bruce Sterling’s Schismatrix, but still the familiar species we see around us today, much as was the crew of the original Star Trek.

As the figure on which the success of these books rests, James Holden exhibits sufficiently brawny and empathetic shoulders. He’s a cross between Captain Kirk (that first name is a tipoff), Han Solo, and Heinlein’s “Competent Man.” He suffers, he sacrifices, he has weak moments and victories, but in the end he always does the right thing for himself, his friends, and civilization. His love affair with Naomi renders him even more likable and reader-friendly.

In Book 2, Caliban’s War, Holden and his crew are employed by the OPA to find a missing child whose fate seems linked to an escaped remnant of the protomolecule. Holden shuts down a suspicious firm, Mao-Kwikoski Mercantile, that was playing with alien fire, becoming famous in the process and making a bad enemy that will appear in the next book. Holden must also weigh his allegiance to OPA with the prospect of taking his ship and pals freelance, at a moment when ghosts of the past begin to mysteriously haunt.

The third Expanse installment, Abbadon’s Gate, reveals that the Venus entity has spawned, leaping outward to form “the Ring,” a mysterious artifact out around Uranus. Holden is sent to investigate the Ring, but finds himself sabotaged by Julie Mao’s vengeful sister, Clarissa, and forced to intermediate among all other factions. The book concludes with the revelation that within the Ring lie stellar possibilities for human expansion throughout the universe. Yet the eternal question remains: who created this life-giving force, and why?

A couple of years pass internally before the events of Book 4, Cibola Burn. Settlers have colonized a newfound planet called Ilus. “Squatters” feud with the RCE corporation officially granted the rights to the property. Again, Holden finds himself acting as two-fisted peacemaker in the middle of a shooting match. When it eventuates that the planet Ilus is a giant machine created 2 billion years ago, his mission becomes considerably more complicated and dangerous.

At this point the veteran reader will be acclimated to the many pleasures of the series. Intense battle scenes alternate with Realpolitik. Ancient Forerunner mysteries, resonant with groundbreaking work by Andre Norton and Charles Sheffield, lurk on the edges of human foibles. Motifs repeat like pleasing song structures. Holden has to have a good cup of coffee before facing the latest challenge. The Rocinante takes a beating, then gets repaired. Amos is Chewbacca to Holden’s Solo. Or are they Robert Parker’s Hawk and Spenser, with Naomi as their Susan Silverman, dispensing moral direction to counterbalance Holden’s bullheadedness? All these signature touches conduce to the consistency-with-variations that is the hallmark of any successful series.

These four books advance their long arc with the seasonal storytelling structures of twenty-first-century top-notch television. Fittingly enough, the SyFy Channel has plans to bring the series to small screens later this very year. And while it is utterly false to say that these books read as if written deliberately for that medium — they are honorable novels first and foremost — it is likewise true to say they should make the transition splendidly.

To its credit, the new volume, Nemesis Games, is a kind of breather, and a change of pace. It dials back some of the macrolevel space opera and gets down to smaller scales, relatively speaking. (If you agree that the partial destruction of Earth is small potatoes in the galactic arena.) Hardly any new characters are introduced — Erich, Amos’s childhood neighbor, now a gang lord, is one such, and a winner — and the author proves himself boldly willing to break some old toys and upset the applecart.

Right away, a huge change. Holden and pals are back from Ilus, and with the Rocinante in drydock at OPA facilities the crew is free to disperse, allowing Corey to hone the natures of the three members who have stood somewhat in Holden’s shadow.

Alex goes to Mars to look up his former wife. Amos goes to Earth to mourn a woman integral to his past. And Naomi is unexpectedly summoned to Ceres, an asteroid city. Holden, missing his buddies, must content himself with hanging out with OPA leader Fred Johnson, with whom he has had some issues in the past.

These four parallel storylines fit together with jigsaw-piece perfection, and a unique foil in Naomi’s ex-lover, Marco Inaros, who has kidnapped her on Ceres. Marco has foreseen that human expansion into other star systems will deprive his beloved Asteroid Belt culture of needed resources, and that the OPA government is doing nothing to prevent this. And so he forges a radical terrorist organization intent on taking out Earth and shutting down the Ring. (Parallels with the Middle East and ISIS are strictly intentional, I wager.) He issues a solar system−wide bombastic speech upon the “success” of his interplanetary bombing, after which Alex wryly comments: “It probably sounded good in his head. . . . And really, when your prelude is you kill a couple billion people, anything you say is going to sound a little megalomaniacal and creepy, right?”

Nemesis Games ends differently from its predecessors, by leaving the new dynamics instituted by Marco’s tipping the table in a kind of midair suspension. A throwaway newscast at book’s end adds to the sense that Corey — or, to resume the reality, Abraham and Franck — envisioned a plot this time around just a little too big to be wrapped up nicely in one volume.

But with these stout, engaging, inventive, and truly fun novels emerging at an annual clip, thus keeping the noble tradition of space opera alive and healthy, we readers will have to buffer our anticipation, secure in the knowledge that the next installment will take us once again someplace special among the stars.