As I watched, several more pinwheels attached themselves. "And these assemblers make the actual camera units?"

"Correct." He typed again. I saw a new image. "This is our target micromachine, the final camera. You've seen the bloodstream version. This is the Pentagon version, quite a bit larger and designed to be airborne. What you're looking at is a molecular helicopter."

"Where's the propeller?" I said.

"Hasn't got one. The machine uses those little round protrusions you see there, stuck in at angles. Those're motors. The machines actually maneuver by climbing the viscosity of the air."

"Climbing the what?"

"Viscosity. Of the air." He smiled. "Micromachine level, remember? It's a whole new world, Jack."

However innovative the design, Ricky was still bound by the Pentagon's engineering specs for the product, and the product wasn't performing. Yes, they had built a camera that couldn't be shot down, and it transmitted images very well. Ricky explained it worked perfectly during tests indoors. But outside, even a modest breeze tended to blow it away like the cloud of dust it was. The engineering team at Xymos was attempting to modify the units to increase mobility, but so far without success. Meanwhile the Department of Defense decided the design constraints were unbeatable, and had backed away from the whole nano concept; the Xymos contract had been canceled; DOD was going to pull funding in another six weeks. I said, "That's why Julia was so desperate for venture capital, these last few weeks?"

"Right," Ricky said. "Frankly, this whole company could go belly up before Christmas."

"Unless you fix the units, so they can work in wind."

"Right, right."

I said, "Ricky, I'm a programmer. I can't help you with your agent mobility problems. That's an issue of molecular design. It's engineering. It's not my area."

"Um, I know that." He paused, frowned. "But actually, we think the program code may be involved in the solution."

"The code? Involved in the solution to what?"

"Jack, I have to be frank with you. We've made a mistake," he said. "But it's not our fault. I swear to you. It wasn't us. It was the contractors." He started down the stairs. "Come on, I'll show you."

Walking briskly, he led me to the far side of the facility, where I saw an open yellow elevator cage mounted on the wall. It was a small elevator, and I was uncomfortable because it was open; I averted my eyes. Ricky said, "Don't like heights?"

"Can't stand them."

"Well, it's better than walking." He pointed off to one side, where an iron ladder ran up the wall to the ceiling. "When the elevator goes out, we have to climb up that." I shuddered. "Not me."

We rode the elevator all the way up to the ceiling, three stories above the ground. Hanging beneath the ceiling was a tangle of ducts and conduits, and a network of mesh walkways to enable workers to service them. I hated the mesh, because I could see through it to the floor far below. I tried not to look down. We had to duck repeatedly beneath the low-hanging pipes. Ricky shouted over the roar of the equipment.

"Everything's up here!" he yelled, pointing in various directions. "Air handlers over there! Water tank for the fire sprinkler system there! Electrical junction boxes there! This is really the center of everything!" Ricky continued down the walkway, finally stopping beside a big air vent, about three feet in diameter, that went into the outer wall.

"This is vent three," he said, leaning close to my ear. "It's one of four main vents that exhausts air to the outside. Now, you see those slots along the vent, and the square boxes that sit in the slots? Those are filter packs. We have microfilters arranged in successive layers, to prevent any external contamination from the facility."

"I see them…"

"You see them now," Ricky said. "Unfortunately, the contractor forgot to install the filters in this particular vent. In fact, they didn't even cut the slots, so the building inspectors never realized anything was missing. They signed off on the building; we started working here. And we vented unfiltered air to the outside environment."

"For how long?"

Ricky bit his lip. "Three weeks."

"And you were at full production?"

He nodded. "We figure we vented approximately twenty-five kilos of contaminants."

"And what were the contaminants?"

"A little of everything. We're not sure of exactly what."

"So you vented E. coli, assemblers, finished molecules, everything?"

"Correct. But we don't know what proportions."

"Do the proportions matter?"

"They might. Yes."

Ricky was increasingly edgy as he told me all this, biting his lip, scratching his head, avoiding my eyes. I didn't get it. In the annals of industrial pollution, fifty pounds of contamination was trivial. Fifty pounds of material would fit comfortably in a gym bag. Unless it was highly toxic or radioactive-and it wasn't-such a small quantity simply didn't matter. I said, "Ricky, so what? Those particles were scattered by the wind across hundreds of miles of desert. They'll decay from sunlight and cosmic radiation. They'll break up, decompose. In a few hours or days, they're gone. Right?"

Ricky shrugged. "Actually, Jack, that's not what-"

It was at that moment that the alarm went off.

It was a quiet alarm, just a soft, insistent pinging, but it made Ricky jump. He ran down the walkway, feet clanging on the metal, toward a computer workstation mounted on the wall. There was a status window in the corner of the monitor. It was flashing red: PV-90 ENTRY.

I said, "What does that mean?"

"Something set off the perimeter alarms." He unclipped his radio and said, "Vince, lock us down."

The radio crackled. "We're locked down, Ricky."

"Raise positive pressure."

"It's up five pounds above baseline. You want more?"

"No. Leave it there. Do we have visualization?"

"Not yet."

"Shit." Ricky stuck the radio back on his belt, began typing quickly. The workstation screen divided into a half-dozen small images from security cameras mounted all around the facility. Some showed the surrounding desert from high views, looking down from rooftops. Others were ground views. The cameras panned slowly.

I saw nothing. Just desert scrub and occasional clumps of cactus.

"False alarm?" I said.

Ricky shook his head. "I wish."

I said, "I don't see anything."

"It'll take a minute to find it."

"Find what?"

"That."

He pointed to the monitor, and bit his lip.

I saw what appeared to be a small, swirling cloud of dark particles. It looked like a dust devil, one of those tiny tornado-like clusters that moved over the ground, spun by convection currents rising from the hot desert floor. Except that this cloud was black, and it had some definition-it seemed to be pinched in the middle, making it look a bit like an old-fashioned Coke bottle. But it didn't hold that shape consistently. The appearance kept shifting, transforming. "Ricky," I said. "What are we looking at?"

"I was hoping you'd tell me."

"It looks like an agent swarm. Is that your camera swarm?"

"No. It's something else."

"How do you know?"

"Because we can't control it. It doesn't respond to our radio signals."

"You've tried?"

"Yes. We've tried to make contact with it for almost two weeks," he said. "It's generating an electrical field that we can measure, but for some reason we can't interact with it."

"So you have a runaway swarm."

"Yes."

"Acting autonomously."

"Yes."

"And this has been going on for…"

"Days. About ten days."

"Ten days?" I frowned. "How is that possible, Ricky? The swarm's a collection of micro-robotic machines. Why haven't they decayed, or run out of power? And why exactly can't you control them? Because if they have the ability to swarm, then there's some electrically mediated interaction among them. So you should be able to take control of the swarm-or at least disrupt it."