Cloud was why the Griffins had come here. At the edges of the zone lit by Slipstream, the air cooled and condensation began. White mist in all its shapes made a wall here separating the sunlit realm from the vast empty spaces of winter. This was the frontier. Here you could hide all manner of things—secret projects, for instance.

The town continued to turn and now sky opened out beyond the barrier of mist—sky with no limits, either up, down, or to either side. Two distant suns carved out a sphere of pale air from this endless firmament, a volume defined by thousands upon thousands of clouds in all shapes and sizes, most of them tinged with dusk colors of rose and amber. There were ragged streamers indicating currents and rivers of air; puffballs and many-armed star shapes; and many miles away, its outlines blurred by intervening dust and mist, a mushroom head was forming as some current of cold impacted a mass of moist air. Below and above, walls of white blocked any further view, while whatever lay on the other side of the suns was obscured by dazzle and golden detail.

As it radiated through hundreds of miles of air, that light would fade and redden, or be shadowed by the countless clouds and objects comprising the nation of Aerie. If you traveled inward or up to civilized spaces, the light from other distant suns would begin to brighten before you ran out of light from yours; but if you went down or back, you would eventually reach a point where their light was completely obscured. There, a creeping chill took over. In the dark and cold, nothing grew. There began the volumes of winter that made up much of the interior of the planet-sized balloon of air, called Virga, where Hayden lived.

Gavin Town hovered at the very edge of civilization, where the filtered light of distant fires could barely keep crops alive. It wasn't lonely out here, though; above, below, and all about hung the habitations of Man. Three miles up to the left, a farm caught the suns' light: within a net a hundred feet across, the farmer had garnered pulverized rock and soil, and was growing a crop of yellow canola. Each plant clutched its own little ball of mud and they all tumbled about slowly, catching and losing the light in one another's shadow. The highway that passed near the farm was busy, a dozen or more small cars sailing along guided by the rope that was the highway itself. The rope extended off into measureless distance, heading for Rush. Below and to the right, a sphere of water the size of a house shimmered, its surface momentarily ridged by a passing breeze.

Hayden could see a school of wetfish swirling inside the sphere like busy diamonds.

There was way too much to take in with a single glance, so Hayden almost didn't spot the commotion. Motion out of the corner of his eye alerted him; leaning over the railing and sighting left along the curving wall of the town, he saw an unusually dense tangle of contrails. The trails led back in the direction of the sun and as he watched, three gleaming shapes shot out of the cloud and arrowed in the same direction.

Strange.

Just as he was wondering what might be happening, the gravity bell rang again. Hayden pushed himself back from the rail and ran for the main street. It wouldn't do for somebody else to get the bikes running after he'd promised Miles he'd be there.

The stairwell to the gravity engines led off the center of the street. Gravity was a public service and the town fathers had insisted on making its utilities both visible and accessible to everyone. Consequently, Hayden was very surprised when he clattered down the steps into the cold and drafty engine room and found nobody there.

Bike number two still hung from its arm above the open hatchway in the floor. It wasn't a bike in the old gravity-bound sense; the fan-jet was a simple metal barrel, open at both ends, with a fan in one end and an alcohol burner at its center.You spun up the fan with a pair of pedals and then lit the burner, and you were away. Hayden's own bike lay partly disassembled in the corner. He'd been meaning to get it running tonight.

When started and lowered through the hatch, bikes one and two would produce enough thrust to spin Gavin Town back up to a respectable five revolutions per minute. This had to be done once or twice a day so normally the engine room would have somebody in it either working, topping up the bike's tanks, or doing maintenance.

Certainly if the gravity bell rang, somebody would always be here in seconds and the bike operational in under a minute.

The wind whistled through the angled walls of the room. Hay-den heard no voices, no running feet.

After a few seconds, though, something else came echoing up through the floor. Somewhere within a mile or two, an irregular popping had started.

It was the unmistakable sound of rifle fire.

A CRACKING ROAR shook the engine room. Hayden dropped to his stomach to look out the floor hatch, just in time to see a bike shoot by just meters below. It flashed Slipstreamer gold. A second later another that gleamed Aerie green followed it. Then the town had curved up and away and there was nothing out there but empty sky. The firing continued, dulled now by the bulk of the town.

Now he heard pounding footsteps and shouting from overhead. Shots rang out from nearby, making Hayden jump.The volleys were erratic, undisciplined, while in the distance he heard a more even, measured response.

As he ran back up the steps something whistled past his ear and hit the wall with a spang. Splinters flew and Hayden ducked down to his hands and knees, knowing full well that it wouldn't do any good when this section of the town rotated into full view of whoever was firing. The bullets would come straight up through the decking.

He emerged onto the still-empty street and ran to the right, where he'd heard people firing. A narrow alley led to the town's other outer street. He skidded around the corner to face the braveway—and saw bodies.

Six men had taken up firing positions at the rail. All were now slumped there or sprawled on the planks, their rifles carelessly flung away. The wood of the rail and flooring was splintered in dozens of places. There was blood everywhere.

Something glided into view beyond the railing, and he blinked at it in astonishment. The red and gold sails of a Slipstream warship spun majestically there, not two hundred yards below. Hayden could make out the figures of men moving inside the open hatches of the tiling. Beyond it, partly eclipsed, lay another ship, and another. Contrails laced the air between and around them.

Hayden took a step toward the braveway and stopped. He looked at the bodies and at the warships, and took another step.

Something shot past the town and he heard a shout from the empty air outside. Gunshots sounded from below his feet and now a wavering contrail dissipated in the air not ten feet past the railing.

He ran to the braveway and took one of the rifles from the nerveless fingers of its former owner. He vaguely recognized the man as someone who'd visited the inn on occasion.

"What do you think you're doing?" Hayden whirled, to find Miles bearing down on him. The cook's mouth was set in a grim line. "If you poke your head out they're gonna shoot it off."

"But we have to do something!"

Miles shook his head. "It's too late for that. Take it from somebody who's been there. Nothing we can do now except get killed, or wait this out."

"But my mother's at the sun!"

Miles jammed his hands in his pockets and looked away. The sun was the Slipstreamers' target, of course. The secret project had been discovered. If Aerie could field its own sun, it would no longer be dependent on Slipstream for light and heat. Right now, Slipstream could choke out Aerie's agriculture by shading their side of the sun; all the gains that Hayden's nation had made in recent years—admittedly the result of Slipstream patronage—would be lost. But the instant that his parents' sun came on the situation would change. Aerie's neighbors to the up and down, left and right would suddenly find a reason to switch allegiances. Aerie could never defend its sun by itself, but by building it out here, on the edge of darkness, they stood to open up huge volumes of barren air to settlement. That real estate would be a tremendous incentive to their neighbors to intercede. That, at least, had been the plan..