I had been living in western Ireland for twenty-seven years, far from the scientific mainstream. True, I had indulged my own interests and followed progress in related fields through the web, but that did not add up to an ability to serve Seth Parsigian’s needs.

However, it would be unwise to suggest that. Instead I said, “I’ll be glad to help you. But how?”

“First, you can answer a couple of questions. I’m pretty sure I know the answers, but let’s get ’em out of the way. You were a world expert on cloning-don’t go modest on me an’ deny it. Did you ever clone yourself?”

The idea was so ludicrous that in spite of my internal tensions I snorted with laughter. “Clone myself? Certainly not. Do you think the world is ready for a second Oliver Guest?”

“Not ready for the first one, if you ask me. But I wanted to be sure. You see, I knew you were living here and had been for ages, so cloning was a natural thought.”

Not to me. But before I could comment he went on. “All right, tell me this. How much do you know about Sky City and the shield? And have you ever been out there?”

More easy questions, although disquieting ones because of their possible implications. We were moving to an area of expertise where my chances of helping Seth Parsigian were negligibly small. “I know very little about Sky City, and even less about the space shield. Far less, I suspect, than the average interested ten-year-old. I have never been into space, and furthermore I never intend to go there.”

“Don’t be too sure on that last one. How much have you heard about the deaths in Sky City over the past six months?”

“I have heard not one word. Don’t deaths happen all the time during space construction work?”

“Not these deaths. Twelve of ’em. All teenagers. All girls. All beauties. Your personal specialty, an’ you’ve not heard a word? Jeez.” Seth stood up and walked through to stare at the dining hall, with its long, solid oak table that we used only when all my darlings were home. “I hope you got some way of feeding me tonight, Doc, because we gotta talk about those deaths on Sky City, an’ we gotta figure out what’s goin’ on out there. An’ I can tell you, from a standing start that might take us quite a while.”

interlude 1

interlude: Sniffer, Model A.

The Sniffer had been built to serve a single purpose, but in their eagerness to achieve that goal its human creators had overengineered their product. They had intended no more than a robust machine, a versatile and long-lived sensing mechanism able to protect itself in the interstellar environment. Instead they had built an entity that inhabited the hazy boundary between sentience and nonsentience.

Certainly Sniffer-A lacked emotion and a true sense of its own place in the universe. Equally certainly it was self-aware, knowing of and concerned with the protection of its multiple parts. And certainly the Sniffer knew its own history, even if that history consisted only of the catalog of experiences since the probe was launched from Earth orbit.

The internal clock placed pointers at the key events:

The origin, before which there was nothing, not even the markers of time itself.

A few thousand seconds after the origin marked the moment of first acceleration. The Sniffer measured the Doppler frequency shift of Earth’s beacon signal and approved it. As planned, the increase in speed was a uniform ten meters per second squared.

One and a half million seconds after first acceleration, Sniffer-A came to the end of the heliosphere, the great bubble of gas controlled by Sol’s influence. The Sniffer was more than eleven billion kilometers from the Sun, twice as far out as the orbit of Pluto. The event came a little sooner than predicted. The Sniffer added that information to the data stream sent back to Earth and hurtled on its way, still adding to its speed.

Two million seconds after first acceleration, the mirror-matter engine ran out of fuel. The Sniffer had reached the end of acceleration and the beginning of coast phase. Terminal velocity was measured as almost twenty thousand kilometers a second, matching the mission profile to better than one part in a million.

Nothing built by humans had ever traveled so fast. The Sniffer registered small reductions in its speed as the fading gravity field of the distant Sun slowed its progress. The deceleration was in the flight profile, and it called for no remedial action.

The Sniffer checked that the guide star of Alpha Centauri lay directly ahead. Then it banked down into power-conserving mode, with the internal clock speed slowed by a factor of four million. Almost dormant, the spidery structure glided through the void between the stars. The main functions of the mission still lay far in the future.

At four hundred and eighty million seconds, almost fifteen years after launch, the incident particle flux rose above a preset threshold. The Sniffer activated all sensors and began a fine profiling of the medium through which it was now moving. At once it found differences from the projected situation.

The supercooled central brain of Sniffer-A had no circuits that might be described as worriers, but it was built to register, record, and transmit anomalies. The great bow wave of charged particles generated by the Alpha Centauri supernova had been reached ahead of time. Also, the particle mixture was grossly different from that in the mission profile.

The Sniffer began its comparisons. The particle flux was more energetic than anticipated, but that was consistent with a greater overall velocity and early arrival. A more significant oddity lay in the unexpected abundance of nuclei heavier than the protons of bare hydrogen. Everything was too plentiful, from deuterium — too weakly bound to have survived the fires of the supernova — to uranium. Odder yet, the data suggested patterns within the particles, as though the ions were somehow maintaining their exact relative separations over large distances.

Sniffer-A’s analytical powers were confined to a comparison between the observations and the predictions loaded into it before launch. It contained no physical models or programs to perform correlations, and it lacked the concept of a structure that ions or other units might follow as they moved through space.

The data went to the communications channels, for return to Earth and to entities with the power to speculate. The Sniffer flew on. In another year, thirty million seconds on the steady internal clock, the main wave had passed. The flux of particles steadily became less.

The reduction was consistent with the onboard math models. Sniffer-A’s closest equivalent to human contentment came when observations matched a preloaded profile. The Sniffer’s activity level gradually decreased.

One more year, and the power levels were down to preencounter values. Sniffer-A cruised quietly on.

It would coast for another half a century. Then it would rouse itself for one final frantic spell of recording and transmission before plunging to its immolation in the turbulent supernova remnant of Alpha Centauri.