“I think so.” Celine had been expecting something far more complicated, and this seemed remarkably clear and simple. “The star experiences a small impulsive force, applied regularly.”

“No.” Star scowled. “Maybe I shouldn’t have used the pendulum idea. Yer can’t hit a star with a regular squeeze, you have ter do it at intervals that vary with time, or it won’t work — and calculating the times gave us no end of trouble.”

“But the principle’s the same, isn’t it?” Celine was reluctant to abandon her nice mental picture. “I mean, instead of coming regularly, the squeezes come at certain calculated times. And if that goes on long enough, the whole star becomes unstable.”

“It does indeed,” Wilmer said, and Star added, “Becomes unstable, and explodes like a son of a bitch.”

“That makes perfect sense.” But Celine suspected that she was still missing something. “Why did you think I would find it hard to accept?”

“Not that part,” said Wilmer. “I felt sure you’d accept everything so far.”

“So what else is there?” Celine looked from Wilmer to Astarte, who had bent low over her plate, grabbed her veal chop in both hands, and was tearing a big piece off it with those crooked white teeth. “What haven’t you told me?”

Astarte stared at her silently over the lump of bloody meat and went on chewing steadily.

“We haven’t told you the part that’s hard to accept,” Wilmer said. “The oscillatory squeeze process that Star describes works perfectly. It allows us to reproduce every measurement that we’ve made since the beginning of the Alpha C supernova. But there’s something we’ve not discussed.”

He deliberately waited, until Celine said, “What?” She had a hollow feeling in the pit of her stomach, as if her worry button had just been pressed.

“The agent. What is it that can impose such a systematic, exactly timed compressive pulse on a whole star?”

“You mean, what physical process can produce that effect?”

“I wish I meant that, but I don’t.” Wilmer seemed upset, and to Celine that was a bad sign. Wilmer never became uncomfortable when physics was the subject. “We’ve racked our brains, Star and me, trying to come up with a natural explanation for what happened. And we can’t. The timing-sequence of the impulses needed to make Alpha C go pop is so peculiar and improbable, I don’t see how it could possibly arise naturally. Something or somebody produced that sequence by design. Something made that star system go supernova.”

While Celine stared in disbelief, Astarte said, “Tell her the rest. About the gamma pulse and the particle storm.”

“Oh, yes.” Wilmer rubbed the bald patch on the top of his head — already red and inflamed from his previous attentions. “It turns out that the right sequence of impulsive compressions needed to provide a supernova is not radially symmetrical. Certain modes of oscillation must be excited, and that in turn gives preferred directions of emission for gamma rays and for the charged particle beam. Everyone always assumed that the fact that the gamma-ray beam was aimed to hit Earth, twenty-seven years ago, was a piece of pure bad luck.”

“Wasn’t it?” Celine was wondering if she could ever explain to anyone else what Wilmer and Astarte had been saying. Not one of her colleagues had any previous experience with Wilmer, or understood his brilliance and intellectual honesty.

“It wasn’t bad luck,” Wilmer said, and Astarte nodded firmly.

“Calculations show that it can’t be an accident,” she added. “Yer see, the Sun moves at thirty-two kilometers a second relative ter Alpha Centauri. Ter have a narrow gamma-ray beam intersect the position of Sol, twenty-seven years ago, and then ter have the main front of the particle storm hit Sol again, in its new position tens of billions of kilometers away — that’s off the scale on the probability charts.

“Something made Alpha Centauri go supernova. And that same something arranged for the gamma pulse and the particle storm ter run right smack bang into our solar system.”

From the private diary of Oliver Guest.

A Proustian obsession with one’s own past is, to my mind, an indicator of mental illness.

And yet, sometimes, it is necessary.

Seth Parsigian had departed at midday telling me that he was going to “check out ideas” that might solve the problem of my inability to face a trip to Sky City. He did not tell me what those ideas were. I did not ask. Nor did he mention an intention to return. I knew the man. He would be back.

Meanwhile, there were the records. Parsigian left with me a mountain of data and conjectures relating to the twelve murders, together with the less-than-helpful advice “See what you can sift out of it, Doc.”

Sifting, however, was not what I had in mind when I sat down, early the same afternoon, to begin my review of the material that he had left with me. What I sought was that intangible sense of contact, the ineffable touch of another’s mind.

Murders, particularly murders of compulsion, represent consequence rather than cause. They occur as the result of some particular motivation. In my own case, it was-and is-a desire to match mental to physical perfection. What, then, motivated the murderer of teenage girls in Sky City? What had been in his mind before he killed?

I examined once more the known facts of the murders, and found thin gruel. I had the dates, the circumstances and places of death, the physical descriptions, and the names: Myra Skelton, Tanya Bishop, Doris Wu, Cissy Muller, April Jarrow, Brenda Cleve, Lucille DeNorville, Denise Braidley, Julia Vansittart, Elke Edson, Georgina Yang, and Kate Ulrey. What did they have in common?

They were young, they were female, and they were dead.

More informative, perhaps: What did they not have in common? They were of widely variable wealth and social class, from the dirt-poor welders’ daughters Brenda Cleve and Cissy Muller to the rich Myra Skelton and the even richer and royally connected Lucille DeNorville. They were not, as Seth had suggested, all beautiful, at least to my tastes. But who could say how the murderer had seen them? Before I knew that I would have to learn to see through his eyes.

The most significant fact was the wide range in the victims’ ages. April Jarrow had been eight, Doris Wu close to fifteen and a half. Although Seth had remarked that April was big for her age, he’d missed the point. I had studied the photographs and medical reports, and April and Doris lay on opposite sides of the great divide of puberty. This, in turn, seemed to place the murderer’s mind beyond reach of my own, since I would never have thought to approach a prepubescent girl.

Would I?

I have an excellent memory for facts. But how to summon to mind bygone emotional states, sensations past? That must also come from the study of cold, hard facts. Alexander Pope puts it as well as anyone: “Remembrance and reflection, how allied. What thin partitions sense from thought divide.”

As afternoon wore on into long summer evening I put all records to one side, abandoned myself to recollection, and sought the depths of my own past.

The initiating event was clear in my mind. I was in my first year of postdoctoral study, bubbling with the ferment of ideas on the causes of apoptosis that led, five years later and via a circuitous route that I could never have imagined in advance, to a full understanding of cell death and thence to telomod therapy.

The research facility where I worked occupied a full block in the center of Atlanta. And here, for the unseen reader who is presumed to hover at the shoulder of every diarist, I must note that I am talking of a time close to forty years ago. The blooming of postapocalyptic Atlanta lay far in the future, while Atlanta’s first golden age was far vanished in the past. When first created, the Institute for Probatory Therapies sat on choice real estate; by the time I moved there it was totally surrounded by the dark metallic heart of the city. The Scantlings had taken over, and that sect’s insistence on uniformity of dress, diet, appearance, possessions, beliefs, and behavior had created the peculiar form of urban paralysis so characteristic of the second decade of this century.