Charles Stross's The Trade of Queens is the sixth and last book in his Merchant Princes series, which began with The Family Trade in 2004 and continued at the rate of roughly one a year with The Hidden Family (2005), The Clan Corporate (2006), The Merchants' War (2007) and The Revolution Business (2009). These books collectively comprise a single story (rather than a series of smaller, related tales in the manner of Stross's Eschaton or Bob Howard books) which begins when Miriam Beckstein, a thirtysomething Boston tech journalist, learns that, with the aid of an heirloom left to her by her birth mother (believed to have died when she was in infancy), she can cross over into a parallel universe. There the eastern seaboard of the United States has been settled by Romanized (but never Christianized) Vikings, and the territory corresponding to Boston is inside the Gruinmarkt, a kingdom which appears stuck in something like the Middle Ages—except for the machine guns.

Shortly after her first visit, Miriam learns she is not the only "world-walker," but a lost child of a clan of tinkers with a gene for this talent. Not only are they aware of that talent, but they have in fact been crossing over from their universe to Miriam's America for centuries. Moreover, they have put their special skills to profitable use in both those worlds, assisting drug traffickers with their talent for covertly getting goods from point A to point B by cutting in and out of the "wall of worlds," and bringing luxury goods and weapons from the modern world back into their own universe, enabling them to amass vast wealth and influence.

Miriam herself is a considerable prize, representing as she does not just an addition to their limited supply of world-walkers, but a potential mother to still more world-walkers—as well as being the heiress to a fortune and title herself. However, the thoroughly modern Miriam is predictably repulsed by the backwardness of the Gruinmarkt, by the thought of getting involved with drug smugglers who very much act the part of an organized crime family, and by the intentions of the family's elders to not only control her, but use her to advance their various agendas. (Indeed, almost as soon as she arrives, she's well aware of the harsher realities of Gruinmarkt, and it's not long before she's thinking about an effort to drag the clan and the kingdom kicking and screaming into modernity.)

Despite Miriam's distaste for what the Clan do and how they behave, she gets swept up in their intrigues. She is caught between progressives and reactionaries within her family, and a pawn in the game of strategic marriages, as the power struggle within Miriam's family, between families within the Clan, and between the Clan and other aristocrats (who tend to view the Clan as upstarts and worse, witches trucking with "demons from the shadow world") over nothing less than the royal throne itself escalates.

Complicating matters still further, Miriam and company learn of still more parallel universes, with their own dangers and opportunities (in particular, one where North America is occupied by a combination of restive eighteenth-century politics with a steampunk/dieselpunk technological base). Meanwhile, back in the universe where Miriam grew up, the "post-9/11" U.S. security state learns about the Clan's world-walking and starts taking a very active interest in their doings, extending to intelligence and military excursions into the Gruinmarket that quickly escalate to a shooting conflict.

By the start of Trade of Queens, a pregnant Miriam is sitting, uneasily, on the Gruinmarkt's throne as the Clan attempts to assert its control over the kingdom. In the midst of this the Clan's own conservative faction retaliates against the United States for its military's actions (which in The Revolution Business went as far as the detonation of a tactical nuclear weapon in the Clan's world as a demonstration of resolve) by smuggling several small nuclear weapons (stolen from the U.S.'s own arsenal) into Washington D.C. and detonating them. The devastation that results kills the U.S. President (along with eighteen thousand others) and leaves the former Vice-President (with whom the Clan has a long and troubling relationship) in his place. The first item on his agenda is striking back against the Clan as the previous administration did against al-Qaida—and is only the first step in a far bigger scheme. Accordingly, despite Miriam's newly regal standing, survival in the face of an anticipated assault by American forces under the command of neoconservative hardliners becomes the order of the day, complicated by the outbreak of a revolution in New Britain with echoes of 1789.

This is, of course, an unusual mix of elements. However, as those who have read much Stross know, he is an old hand at the hybridization of different genres, subgenres and authorial styles—as with his combination of steampunk, space opera and posthumanism in Singularity Sky (2003), or Len Deighton's Harry Palmer and H.P. Lovecraft's Cthulhu mythos in his Bob Howard tales from The Atrocity Archive (2004) on. Here he draws on H. Beam Piper's Paratime and Roger Zelazny's Chronicles of Amber series.

Many of the concepts and themes on which Stross has built his literary career are also present, from the espionage tradecraft and secret police antics, to the penchant for alternate (and secret) history, to the element of political satire. The same goes for his play with techno-economic systems and the idea of their abrupt transformation in a telescoped evolutionary process, especially as initiated or accelerated by his protagonists. Miriam Beckstein's attempts to break the quasi-medieval Gruinmarkt out of its "development trap" are broadly comparable with Rachel Mansour's mission on Rochard's World in Singularity Sky, or Manfred Mancx and company's antics in the twenty-first century as depicted in Accelerando (2005). The same goes for stylistic touches, like Stross's penchant for allusions that would escape a casual reader of science fiction. ("The sky was the color of a dead laptop display, silver-gray and full of rain," goes the opening line of The Family Trade, in an echo of Neuromancer's famous first words.)

Nonetheless, in contrast with the idea-blizzards represented by the other books discussed above, The Merchant Princes is far less demanding. A movement from the Middle Ages to modernity, even when compressed into a space of two generations, is a far cry from the technological Singularity. The Gruinmarkt confronts the reader with comparatively little world-building to digest, and while Stross develops a clear set of rules about how world-walking works, the speculative physics is rather less formidable than the "applied computational demonology" of the Bob Howard stories, and even then are barely touched on prior to book four.

The emphasis is correspondingly shifted from density and exoticism of concept—which has long been Stross's greatest strength—to plot, story and characters—areas where Stross's performance has been less certain. Part of this would seem to be due to simple commercial considerations, which encourage accessibility at the expense of going all-out on innovation. (On the acknowledgements page of the first book, Stross mentions that his agent "nudged me to make a radical change of direction from my previous novels," with Tor editor David Hartwell encouraging him further along that path.) Additionally, the density and head-spinning weirdness that are hallmarks of much of Stross's best writing are harder to sustain over a longer narrative—and certainly for the two thousand page-length of the series' combined books.

However, Stross's strong suit in The Merchant Princes remains concept. Even "Stross Lite" is recognizably Stross, and his now well-established approach—his effective mixing of disparate ideas, his knack for blending speculative science with fantasy, his eye for sociological detail and the like—brings a good deal of interest to this twist on Zelazny's well-known fantasy series. His embrace of the sort of political critique of the fantasy genre that Michael Moorcock presented in his essay "Epic Pooh" has its interest too, particularly given Miriam's personal response to it. As emphasized in much of the publicity for the books—in which the praise of economist Paul Krugman has been particularly prominent—this is a story about developmental economics, though it is also one about the "War on Terror," adding additional dimensions to the narrative.

Admittedly, there are hits as well as misses on this level. The Gruinmarkt struck me as being more in line with the simplicities of historical fantasy fiction than the actual complexity of the Middle Ages, one cliché I would have liked to see Stross stand on its head. (Miriam's kingdom curiously combines the feudal diffusion of power of the Western Middle Ages with an institutional underdevelopment that made me think rather of pre-Petrine Russia; and while the existence of the serfs is acknowledged, they are also entirely outside the games the aristocrats play, in a way that again seemed all too traditional and simplistic.) There are also some ways in which the Gruinmarkt does not work well as an analog to the development traps in which so much of the planet is stuck. The Clan, for instance, never had to stare down the International Monetary Fund or the World Trade Organization over the fostering of the infant industries they might have plausibly cultivated.

All the same, these are comparative nitpicks, and the more significant weaknesses are elsewhere. The first is Stross's pacing. His plotting is suitably elaborate, but the start of the series is slow, certainly in comparison with the reader's swift immersion in the events of Zelazny's ruggedly pulpy Chronicles. Indeed, while periodically offering an interesting bit to hold the reader's attention the first two books come across as largely set-up, and in the third book Miriam actually does next to nothing. (Stross actually addressed the complaints about this in his recent blog post on the conclusion of the series, "Post-Mortem," in which he attributes such unevenness to the redivision of the story from four fat books to a half dozen slimmer ones.)

The second is the flatness of the characters, which is easy to overlook in a tightly constructed, idea-driven story, but is at times quite obvious here because of the sprawling, epic approach. Miriam is no exception, and this fact, along with her staggering mix of talents (not just world-walking, but her implausibly Renaissance-person-like array of medical, journalistic, engineering, business and other expertise), the ease with which she attracts helpers and admirers, and the grandiose roles she assumes in not just one but two worlds where women are ordinarily marginalized, make her something of a wish-fulfillment character (though Stross is otherwise successful in keeping his story from assuming a wish-fulfillment quality). Quite a few of the Clan members are so thinly sketched as to be interchangeable (as with the rather generic Olga and Brilliana, even after a half dozen books). The government bureaucrats who respond to the discovery of the Family's drug smuggling and other activities in the United States (Miriam's ex-boyfriend Mike Fleming included) are mostly cardboard figures, merely existing to move the plot along.

Nonetheless, the pacing is less of a problem with the whole series now available, and readers not stuck having to wait a year or more for the release of the next installment. Additionally, the pace picks up after the mid-point (something that also compensates for the weak characterizations), and Trade of Queens is easily the briskest read in The Merchant Princes. Indeed, where some of the earlier books felt padded, an extra chapter or two would actually have helped flesh out the narrative in this case. As things are, however, Stross effectively builds tension as the clock ticks down toward a hopeless confrontation between the Clan and its superpower opponent, while the scientific tweaks and the satirical elements (like the Pentagon's application of the Clan's world-walking ability to its heavy weapons systems, and the public and international outcry that follow when news of the parallel universes goes public, both quite sharply written in Queens) succeed in lifting even the previously bland techno-thriller-style bits above the level of generic security state procedural. The upheaval in New Britain, as seen from the standpoint of Miriam's sometime collaborator Erasmus Burgeson (who, courtesy of Miriam's books, is all too aware of how revolutions go awry), which I found engaging from quite early on, remains so. The conclusion brings events in these three universes together successfully, even if the nature of said conclusion is not entirely unprecedented in Stross's fiction; and while it may appear to abandon the series' central theme up to this point, it can also be read as nothing more and nothing less than the darkest possible take on it.

At its best, Trade of Queens offers the zaniness and zip Stross presented in stories like "A Colder War" and "Missile Gap." This all makes for a more than satisfactory close to a series which, for all its weaknesses, I found to be worth the read, and indeed, worthy of another look from readers who may have felt let down by the earlier volumes.

Nader Elhefnawy has taught literature at several colleges, including the University of Miami. He reviews and writes about science fiction for several publications, and on his blog, Raritania.