On his blog, author Karl Schroeder has referred to his latest novel, The Sunless Countries, as "the fourth book in the Virga trilogy." He clarifies this oxymoron by saying that the first three books consisted of a single narrative arc, while this fourth is a standalone pendant allowing him to explore a different portion of his universe.
As such, it might very well serve as a good gateway for newbies into the fascinating Virga cosmos, an enormous, air-filled fullerene balloon in the Vegan star system containing worldlets of varying size that center around the "sun of suns," Candesce. It's a Boschian landscape, full of rich cognitive estrangement, and Schroeder gets the most out of his conceptual playground, with taut prose and wild plotting.
He starts out this volume with a winning tactic: introducing a new protagonist full of charm, intelligence, humility and bravery. Leal Mapeth is a teaching assistant in the history department at a university in her home city of Sere. Sere is undergoing a political realignment, and that adds plenty of perilous intrigue to Leal's life. But the advent of the enigmatic "winter wraiths," the arrival of Hayden Griffin (a heroic fellow we've met in earlier volumes) and the recurrence of a "worldwasp," an alien from the timeless history of Virga's founding, all conduce toward an even more hectic, dangerous and exciting period in Leal's young life.
As Leal embarks on a series of wild, thrilling adventures with Hayden, seeking to save her city from its various troubles and to benefit the human race en masse, Schroeder exploits the bizarre physics of Virga to exhibit a variety of exotic tableaux, including a dangerous intercity realm of giant insects, mold and other parasitic dangers. The various cultures of Virga emerge from these same cosmic constraints with splendid logic and surprise. Yet Schroeder never neglects the homey aspects of human social life: one of the first things Leal wants to do when she visits a sun-splashed world for the first time is to go shopping.
Ultimately, much of Leal's progress and success relies on the secrets contained in a mysterious book named the Polyhistoria. This fourth book in Schroeder's series functions in the same manner as this arcane fictional tome, revealing treasures the earlier three did not contain, revelations about Virga's place in the "foam of worlds," and as such it is essential to Schroeder's artistic scheme and to the full enjoyment of this saga.