In the sealed chamber, furious activity boomed and echoed, a steady process of moving belts, whirring machine-tools, fast-moving mechanical supervisors. At one end, a steady flow of raw materials entered the line; at the far end, the final product was whipped off, inspected and crammed into a conveyer tube.

All this was visible for a split second; then the intrusion was discovered. Robot relays came into play. The blaze of lights flickered and dimmed. The assembly line froze to a halt, stopped in its furious activity.

The machines clicked off and became silent.

At one end, a mobile unit detached itself and sped up the wall toward the hole O’Neill and Morrison had cut. It slammed an emergency seal in place and expertly welded it tight. The scene below was gone. A moment later the floor shivered as activity resumed.

Morrison, white-faced and shaking, turned to O’Neill. “What are they doing? What are they making?”

“Not weapons,” O’Neill said.

“That stuff is being sent up”—Morrison gestured convulsively—“to the surface.”

Shakily, O’Neill climbed to his feet. “Can we locate the spot?”

“I—think so.”

“We better.” O’Neill swept up the flashlight and started toward the ascent ramp. “We’re going to have to see what those pellets are that they’re shooting up.”

The exit valve of the conveyor tube was concealed in a tangle of vines and ruins a quarter of a mile beyond the factory. In a slot of rock at the base of the mountains the valve poked up like a nozzle. From ten yards away, it was invisible; the two men were almost on top of it before they noticed it.

Every few moments, a pellet burst from the valve and shot up into the sky. The nozzle revolved and altered its angle of deflection; each pellet was launched in a slightly varied trajectory.

“How far are they going?” Morrison wondered.

“Probably varies. It’s distributing them at random.” O’Neill advanced cautiously, but the mechanism took no note of him. Plastered against the towering wall of rock was a crumpled pellet; by accident, the nozzle had released it directly at the mountainside. O’Neill climbed up, got it and jumped down.

The pellet was a smashed container of machinery, tiny metallic elements too minute to be analyzed without a microscope.

“Not a weapon,” O’Neill said.

The cylinder had split. At first he couldn’t tell if it had been the impact or deliberate internal mechanisms at work. From the rent, an ooze of metal bits was sliding. Squatting down, O’Neill examined them.

The bits were in motion. Microscopic machinery, smaller than ants, smaller than pins, working energetically, purposefully—constructing something that looked like a tiny rectangle of steel.

“They’re building,” O’Neill said, awed. He got up and prowled on. Off to the side, at the far edge of the gully, he came across a downed pellet far advanced on its construction. Apparently it had been released some time ago.

This one had made great enough progress to be identified. Minute as it was, the structure was familiar. The machinery was building a miniature replica of the demolished factory.

“Well,” O’Neill said thoughtfully, “we’re back where we started from. For better or worse . .. I don’t know.”

“I guess they must be all over Earth by now,” Morrison said, “landing everywhere and going to work.”

A thought struck O’Neill. “Maybe some of them are geared to escape velocity. That would be neat—autofac networks throughout the whole universe.” Behind him, the nozzle continued to spurt out its torrent of metal seeds.

It would be wise to explain what Courtland was doing just before the doorbell rang.

In his swank apartment on Leavenworth Street where Russian Hill drops to the flat expanse of North Beach and finally to the San Francisco Bay itself, David Courtland sat hunched over a series of routine reports, a week’s file of technical data dealing with the results of the Mount Diablo tests. As research director for Pesco Paints, Courtland was concerning himself with the comparative durability of various surfaces manufactured by his company. Treated shingles had baked and sweated in the California heat for five hundred and sixty-four days. It was now time to see which pore-filler withstood oxidation, and to adjust production schedules accordingly.

Involved with his intricate analytical data, Courtland at first failed to hear the bell. In the corner of the living room his high-fidelity Bogen amplifier, turntable, and speaker were playing a Schumann symphony. His wife, Fay, was doing the dinner dishes in the kitchen. The two children, Bobby and Ralf, were already in their bunk beds, asleep. Reaching for his pipe, Courtland leaned back from the desk a moment, ran a heavy hand through his thinning gray hair … and heard the bell.

“Damn,” he said. Vaguely, he wondered how many times the demure chimes had sounded; he had a dim subliminal memory of repeated attempts to attract his attention. Before his tired eyes the mass of report sheets wavered and receded. Who the hell was it? His watch read only nine-thirty; he couldn’t really complain, yet.

“Want me to get it?” Fay called brightly from the kitchen.

“I’ll get it.” Wearily, Courtland got to his feet, stuffed his feet into his shoes, and plodded across the room, past the couch, floor lamp, magazine rack, the phonograph, the bookcase, to the door. He was a heavy-set middle-aged technologist, and he didn’t like people interrupting his work.

In the halls stood an unfamiliar visitor. “Good evening, sir,” the visitor said, intently examining a clipboard; “I’m sorry to bother you.”

Courtland glared sourly at the young man. A salesman, probably. Thin, blond-haired, in a white shirt, bow tie, single-breasted blue suit, the young man stood gripping his clipboard in one hand and a bulging black suitcase with the other. His bony features were set in an expression of serious concentration. There was an air of studious confusion about him; brow wrinkled, lips tight together, the muscles of his cheeks began to twitch into overt worry. Glancing up he asked, “Is this 1846 Leavenworth? Apartment 3A?”

“That’s right,” Courtland said, with the infinite patience due a dumb animal.

The taut frown on the young man’s face relaxed a trifle. “Yes, sir,” he said, in his urgent tenor. Peering past Courtland into the apartment, he said, “I’m sorry to bother you in the evening when you’re working, but as you probably know we’ve been pretty full up the last couple of days. That’s why we couldn’t answer your call sooner.”

“My call?” Courtland echoed. Under his unbuttoned collar, he was beginning to glow a dull red. Undoubtedly something Fay had got him mixed up in; something she thought he should look into, something vital to gracious living. “What the hell are you talking about?” he demanded. “Come to the point.”

The young man flushed, swallowed noisily, tried to grin, and then hurried on huskily, “Sir, I’m the repairman you asked for; I’m here to fix your swibble.”

The facetious retort that came to Courtland’s mind was one that later on he wished he had used. “Maybe,” he wished he had said, “I don’t want my swibble fixed. Maybe I like my swibble the way it is.” But he didn’t say that. Instead, he blinked, pulled the door in slightly, and said, “My what!”

“Yes, sir,” the young man persisted. “The record of your swibble installation came to us as a matter of course. Usually we make an automatic adjustment inquiry, but your call preceded that—so I’m here with complete service equipment. Now, as to the nature of your particular complaint…” Furiously, the young man pawed through the sheaf of papers on his clipboard. “Well, there’s no point in looking for that; you can tell me orally. As you probably know, sir, we’re not officially a part of the vending corporation… we have what is called an insurance-type coverage that comes into existence automatically, when your purchase is made. Of course, you can cancel the arrangement with us.” Feebly, he tried a joke. “I have heard there’re a couple of competitors in the service business.”