And so an entirely unrelated narrative weaves its way through the VR story. While the programmers build Rousseau's jungle, Tai Martin, an American hostage in Lebanon, savors a hard-won concession from his captors -- a daily half-hour of freedom to move around his room as he pleases:

You pace about, astonished. From the once-mythical far side of this cube, you look back across the ocean of air. Seeing your corner like this, from a distance -- your mattress, radiator, chain; the grubby country that swallowed you entire -- it looks bounded, known, livable.

A dirty, windowless room in Beirut becomes the novel's ground zero. Martin's desperate and brilliant expedients to stay sane and human (drawn by Powers from many memoirs by political hostages) are as compelling as any of the book's computer wonder stories. His struggle -- to find world-making tools in a cruelly deprived environment -- is the thought experiment at the book's core, the dark background against which the flashy VR technology is projected.

"We're all scientists … every person running this little experiment in being alive," one character observes. The problem to be solved is an inhospitable world not of our own making. The experiment -- to remake it so as to make ourselves at home in it -- is consciousness, the ability to see "the miraculous density of day's data structure" in "a place wide enough to house human restlessness."

Although sometimes heart rending, particularly in the Beirut sections, "Plowing the Dark" is by and large a work of great charm animated by the simple joy of making things. "You type some words," says Stevie, a poet turned systems engineer, "the inner name of the thing. You describe how you want it. You build a topical outline of its behavior. Then you run the description, and there the idea is. Actual, working …"

I don't suppose any real VR lab ever tried to grow Rousseau's vegetation, or to rebuild Van Gogh's room in Arles and open the window's heavy shutters. But what a lovely thought, and what lovely language Powers bends around the imagined programming tasks:

Collision had already cost the team a tidy sum of man-months. It wasn't enough for a garden-variety mushroom sprouting in the Cavern simply to look like one. Even a toadstool needed heft and weight and resistance. A simulated object had to bend or droop or bruise or any of several dozen other verbs that real things did when bumped up against … Various variables toted up mass and speed and English, calculating the thresholds between bounce and break, between shatter and slide and spin.

Think of the old Windows screen saver that sets two delicate polygons rotating in space as their angles narrow and widen and their colors traverse the spectrum. And then imagine a blooming, buzzing world in three dimensions, every object enabled to act to the extent of its attributes -- its mass, its speed, its … English. Powers' fertile, restless English is endlessly plastic, infinitely ready to reshape itself around whatever world he's exploring at the moment. Wildly fecund in "The Gold Bug Variations," nearly desperate in "Operation Wandering Soul," his language here is as hard and bright as the syntax of Java or C++.

A smaller-scale work than, say, "Gain," "Plowing the Dark" remains rooted in its historical moment and insistent on human perception as the measure of things. Although imbued with the horrors of war and the unholy technologies of unmaking the world, it feels almost optimistic in its resolution, refreshing in its evocation of a time less cyberselfish than our own. It's a chamber work, really, this meditation on rooms and other spaces, this smart, sweet, harrowing novel that reminds us how much the human prospect depends upon the homes -- virtual and otherwise -- that we build for ourselves on Earth.

Maya Angelou reads from "The Heart of a Woman"