“And they seem to be motivated not by expansion for its own sake, as we are, but by a desire to understand the fine-tuning of the universe. Why are we here? You see, Ensign Pirius, there is only a narrow range of physical possibilities within which life of any sort is possible. We think the Ghosts were studying this question by pushing at the boundaries—by tinkering with the laws which govern us all.”

“But that made them dangerous.”

“Yes,” Mara said. “An enemy who can use the laws of physics as a weapon is formidable. But they developed their capabilities, not as some vast weapons program, but for their own species imperative. Until they ran up against humans, it had nothing to do with us. . . .”

Pirius sensed movement behind him. A Silver Ghost hovered massively, a few meters away, just above the ice surface.

Mara said quickly, “It’s only the Sink Ambassador. It must have followed us. It’s probably curious.”

“Curious? You talk as if it’s a child.” Pirius saw himself reflected in the Ghost’s complacent hide. “You,” he said. “You are the Sink Ambassador?”

“That is what I am called.”

“Is she right? That you Ghosts follow your own logic, that you care nothing for humans?”

“I don’t know,” the Ghost said. “I have no reliable data on the past.”

Mara said dryly, “These new Ghosts won’t believe a word we say about their history. Maybe they’re right not to.”

“We destroyed you,” Pirius said. “And we brought you back. Everything about you is in our power.”

“True. But that doesn’t alter my perception of you.”

Fists clenched, Pirius stepped up to the Ghost. Suddenly all the complex emotions he had been feeling—his inbred hatred of the Ghosts, his confusion at the reaction of Mara and the others, all that had struck him so overwhelmingly since the day his own future self had docked at Arches—welled up in him. And here was a Silver Ghost, right in front of him. He said on impulse, “Perhaps Mara is right. Perhaps I must learn about you, as you have learned about humans.”

Mara was disturbed. “What are you doing, Ensign?”

“Remove your hide. Disassemble yourself. Show me what you are.”

Mara laid a gloved hand on Pirius’s arm. Her eyes were bright with anger. “I knew I shouldn’t have brought you here.”

Pirius shook her off. “I command this Ghost. I am human.”

The Ghost was motionless, save for its usual subtle wafting, and Pirius, shaking with anger, wondered what he would do if the Ghost refused. He remembered his training on how to fight a Ghost. That hide was tough, but if you used all your strength you could get your knife into it, and then you could use the Ghost’s own rotation against it and open it up. . . .