Nilis’s characteristic curiosity cut in. He stood before the Ghost, hands on hips, rheumy eyes alive with interest. “So,” said Nilis. He held out a liver-spotted hand, as if to stroke the Ghost’s surface; but he thought better of it and pulled back, curling his fingers. “Which one are you?”

“I am the one you call the Ambassador to the Heat Sink.” The Ghost’s chill contralto voice seemed heavily artificial in this small sick-bay room. “We met on Pluto.”

“Of course we did. I should have guessed it was you. But how would I know if you were lying, if you’re a different Ghost entirely? Hah!”

The Ghost didn’t respond. Darc, still as a statue, was almost as unreadable.

Nilis went on, “And what are you doing here?”

“It’s come to see me, Commissary,” Torec said gently.

Nilis made a mock bow.

Torec plucked up her courage and faced the Ghost. She could see herself in its hide, a distorted image of a head and shoulders, clutching her med-blanket. “Maybe that’s what’s so scary about you,” she said aloud.

The Ghost said, “I do not understand.”

“That every time I look at a Ghost, I see myself.”

The Ghost rolled slowly, slight imperfections on its surface marking its movements. “Identity is a complex concept which does not translate well across cultures.”

Torec said, “Why have you come to see me, Sink Ambassador?”

“Because your project is failing,” it said.

Nilis nodded. “Yes, yes. We are battling the instability of your gravastar shield, it can’t be denied.”

Darc snorted. “And it’s a fundamental flaw. The spherically symmetric solution of the equations — a complete gravastar, a shell surrounding a ball-shaped pocket universe — would be stable. Your half- and-half solution, a spherical cap preceding a pocket universe that matches to ours asymptotically, is analytically complete, but is not stable.” He gave a thin-lipped grin. “Oh, don’t look so shocked, Commissary. Even Navy grunts know a little math. The problem is simple: instability. You have your pilot balancing a ten-meter pole on the palm of her hand; she can run as fast as she likes, but sooner or later she will fall.”

The Ghost said, “But we have a solution.”

Nilis and Darc both turned to face the Ghost, startled.

Torec smiled. “So that’s why you’ve come. You weren’t concerned about my health at all.”

The Ghost seemed to think that over. “No offense.”

Nilis gaped. “Did a Silver Ghost just make a joke?”

Darc said sternly, “You say you have a solution. Describe it.”

The Ambassador rolled, and Virtual images scrolled in the air. Torec recognized a map of the phase space of a system. It was a schematic diagram of the possible states of the gravastar shield. It looked like a slice of a rolling landscape, with valleys, peaks, and plains, and it was marked with contours that showed regions of chaos and stability, attractors and poles.

“The trick,” said the Ghost, “is to use the instability, not to fight it. You are trying to emulate the stability of the strongest attractor, which is the spherically symmetric solution here.” A point on the map winked red. “So you allow the shield to form at low velocities, or even when the projector is stationary. You find an equilibrium, but it is not stable. Then when you try to fly, the smallest instability disrupts the solution. Your running child trips on a pebble, Commander, and the pole is dropped.”

Nilis laughed out loud. “You have spent a long time studying human idioms.”

“We have little else to do,” the Ghost said.

“So,” Darc growled, “what do you suggest instead?”

“It would be better to operate the projector when it is being carried at close to lightspeed.”

Nilis frowned. He walked up to the image and poked his finger into its shining innards. “But that would bring us up to this region.” It was the complex border between order and chaos. “The shield would be no more than meta-stable.”

“But solutions in this part of the phase space, on the edge of chaos, would be responsive to small adjustments.”

“Ah.” Nilis nodded. “Which would make the shield more manageable, because it would respond more sensitively; we could control out the instabilities before a catastrophic disruption.”

Darc was visibly unhappy. “How rapidly would we have to react?” He brought up a Virtual of his own, ran some quick calculations. “There,” he said in triumph. “Look at that! Your meta-stable shield will flap like a sheet in a breeze. There’s no way we could react quickly enough to respond to it.”

“Of course you could,” the Ambassador said. “You have arbitrarily high processing speeds available on your ship. Your CTC-processor technology—”

Darc shot to his feet and stalked up to the Ghost, fists clenched. “Is that the game? How do you even know about that? If you think I am going to let you anywhere near the CTC system—”

Nilis said, “Commander, please. We’re simply discussing possibilities.”

Darc remained standing, glaring at the Ghost. “Why are you doing this? Humans destroyed your kind. Why would you help your conquerors?”

“Curiosity,” the Ghost said.

“And nothing else?” Darc asked heavily.

“Nothing. You recreated us at a whim. You could destroy us as easily. We have no hope.”

Darc’s eyes narrowed with suspicion, but he stayed silent.

Nilis was still thinking over the idea. “This would actually simplify the overall design, of course… You don’t seem happy, Ensign.”

Torec said, “I’m a pilot, sir. No pilot likes giving up control.”

“Hmm. I can sympathize with that. And of course this sort of active-control system isn’t without risks. You would go into battle behind an intrinsically unstable system. If the CTC failed, you would die immediately.”

“But we all die one day, Commissary.”

He embarrassed her by allowing his eyes to fill up. “Lethe, this laconic courage — I’m sorry! I can’t get used to it.”

The Ghost said, “You have one more test ship.”

“One more chance,” Nilis said. “The modifications would be straightforward.” He stared at Darc.

Darc held his stubborn stance for a moment, then seemed to give in. “All right. Lethe take this whole plagued project! But what are we to do for a crew?”

Torec sat up straight. “I’m willing to give it another go, sir.”

Nilis said, “I’d expect nothing less. But we must make this crucial trial work. I would suggest that the ensign’s ideal crewmates are in this room.”

Darc stared at him, then at the Ghost, which rolled silently. “You have got to be joking.”

But he wasn’t.

Chapter 27

“The Central Star Mass,” Nilis said. “Isn’t that what you call it, Pirius Blue? The Mass — what a mundane name for a place where you can find ten million stars in a space a few light-years across — a volume in which, at the Galactic vicinity of Sol, you would on average find one. How marvelous, that we feeble humans should have come so far!”

He had called Pirius Blue to the small quarters he had been allocated in Quin’s Officer Country. His face shining with enthusiasm, his long robe as scuffed and threadbare as ever, he bumbled around the room, setting out his data desks on the low table. The Commissary was just as Pirius remembered from the trial, though he seemed older, rather more careworn. But Nilis hadn’t been prepared for Pirius’s new eyes; at first sight he had recoiled, his shock comical.

This wasn’t the real Commissary, of course. Nilis was too busy with his mysterious projects in Sol system to come all the way to the center again in person. This was only a Virtual.

Nilis was still struggling to get political support for his schemes. He said he had forced his way into Quin Base on a pretext. He had managed to persuade his bosses at the Commission for Historical Truth that it was time somebody took a fresh look at the deviant religions sprouting here in the Core. But quizzing This Burden Must Pass about the nature of the Ultimate Observer was not Nilis’s true goal.