Graves would not meet Rebka’s eye. “I sometimes wonder if the ethics we favor are just as local and as limited as our common set of body shapes and thought patterns. The Builders had science truly alien to us. It does not match our worldview. We do not know how they built, or why they built. And yet our scientists tell us that there is only one set of physical laws that govern the whole universe — just as our philosophers tell us that we have one system of universal ethics! I wonder if Builder ethics would prove as alien as their science. Or if they, able to see how we treat our many different species, would not be appalled at our bias and misjudgment.

“I propose that we all have a lesson to learn, Captain, and it is as simple as this: the rules set up by any council must be dynamic. Regardless of the way they are viewed by the average person, they cannot be forever the same, set in stone and steel. We must study them constantly. And we must always ask if they can be improved.”

Graves glared suddenly at Rebka, turned, and ascended the ramp to the upper level of the capsule.

Rebka remained seated and stared after him. There had been a counterpoint in those final sentences, almost of two voices. Was it possible that Julius and Steven Graves were holding some kind of interior dialogue, with Rebka no more than bystander? Maybe Julius wanted to do one thing, and Steven another.

It was preposterous; but no more unlikely than the development of individual consciousness in the mnemonic twin. And if working with Julius Graves on the surface of Quake would be bad, working with an unstable mixture of Julius and Steven would be impossible.

Twins, squabbling for dominance within one braincase? Rebka stood up, noticing as he did so that the deck offered much less pressure on the soles of his feet. His weight was down to a few pounds. They must be closing on Midway Station. He headed for the ramp, wondering if Max Perry was still sitting in frozen contemplation of Quake. More and more, he felt like the keeper of a bunch of talented lunatics.

On his first trip to Quake, Rebka had been quite keen to enter and examine Midway Station. Humans had modified and cannibalized it, but it was still Builder technology, and that made it fascinating. Yet when Max Perry had chosen to bypass it — had been driven to bypass it — Rebka, in his own curiosity about Quake, had not argued with that decision.

Now the urgency to reach Quake was far greater — thirteen Dobelle days to Summertide, according to Rebka’s internal clock; only one hundred and ten hours! Keep moving! — but now Perry insisted on stopping at Midway.

“Take a look for yourself.” Perry pointed at the status board on their capsule. “See the power consumption? It’s too high.”

Rebka looked and could deduce nothing. Nor could Graves. If Perry said things did not seem right, the others had to believe him. There was no substitute for experience, and when they were on the Umbilical, Perry’s knowledge reigned supreme.

“Are we in danger?” Graves asked.

“Not immediate danger.” Perry was rubbing his nose thoughtfully. “But we can’t risk heading down to Quake until we know why the power use is up. We daren’t risk power loss for our own approach. And the central controls are all on Midway Station. We have to stop there and find out what’s happening.”

Under his direction, the capsule had already left its invisible guides and turned toward the misshapen bulk that filled half the sky on their left.

When humans had first discovered it, Midway Station had been an airless, arching vault, three kilometers across and almost empty. The walls were transparent. A man in a space suit could fly to the side facing Opal and detect that he was falling gently in that direction; one strong kick off the glassy outer wall would carry him through the open interior. He would then drift on and on, gradually slowing, until the opposite outer wall finally arrested his motion. The station marked the exact center of mass of the Quake/Opal coupled system.

The Builders’ uses for Midway Station were not understood. That did not matter to most humans. They had filled the open sphere with a set of interlocking pressurized chambers, making it a temporary habitat and a storage facility for everything from thermal boots to freeze-dried food. Responding to some old cave instinct that favored enclosed spaces, they had also covered the external walls with a shiny, opaque monolayer. After four thousand years of Expansion, humans were apparently still uncomfortable with the open endlessness of space.

The capsule moved through a first airlock, then nosed molelike along a dark corridor just wide enough to permit its passage. Two minutes later it came to a cylindrical chamber filled with racks of display equipment and control boards.

Perry waited for a couple of minutes while the interior and exterior pressures were almost matched, then forced open the capsule’s hatch and floated out. By the time the others had followed him he was already at work on one of the displays.

“Here.” He pointed. “Straightforward enough. That’s the problem. Another car was traveling the Umbilical at the same time as us.”

“Where?” Rebka stared at the displays. They showed cameras and monitors all along the length of the Umbilical. He saw nothing.

“No, you won’t see it.” Perry had noticed where Rebka was looking. “The power drain is over now. That means the other capsule isn’t on the Umbilical anymore.”

“So where is it?” Graves asked.

Perry shrugged. “We’ll find out. I hope there’s someone on duty down there. I’m sending an emergency signal.” He was already moving across to a communications unit and tapping in entry codes.

Within twenty seconds Birdie Kelly’s face came onto the screen. He was panting, and his hair was tousled. “Max? Commander Perry? What’s wrong?”

“You can tell us, Birdie. Look at your power draw for the past few hours. We’ve had two capsules in use.”

“That’s right. No problem; we checked and there’s plenty in reserve.”

“Maybe. But there is a problem. That other car didn’t have authorization.”

Birdie’s face was puzzled. “It certainly did. The woman had authorization from you. Personally. Hold one second.”

He disappeared for a few moments from the screen and returned holding a marked sheet. “That’s your sigil — see it? — right there.”

“You let her have a car?”

“Of course I did.” Birdie’s tone switched from defensive to annoyed. “She had authorization, and she must have known the exact Umbilical command codes. If she hadn’t, they’d never have risen one meter above sea level.”

“They?”

“Sure. We assumed you knew all about this. The woman.” Birdie Kelly peered at the sheet. “Darya Lang. With the two aliens. A Cecropian, and another form I didn’t recognize. What’s going on up there?”

“That authorization was bogus, Birdie. My sigil was faked.” Perry glanced at another control board. “We show they’re not on the Umbilical anymore.”

“Right. They’ll be on Quake. I hope they’re having a better time up there than we are here.” The wall behind Kelly shivered and tilted, and a scream of wind sounded through the link. He turned to glance away from the screen for a split second. “Commander, unless there’s something else I can tell you, I have to get off right now.”

“Another storm?”

“Worst ever. We just had a call through the Sling Network, five minutes ago. Spidermonkey is starting to break up. We have an airlift going in, but they’re having trouble landing on the Sling to get people off.”

“Go help there. We’re on our way. Good luck, Birdie.”

“Thanks. We’re going to need it. Same to you.”

Birdie Kelly was gone.

And so was Perry. By the time Rebka and Graves caught up with him he was starting to seal the capsule.

“Nine hours ahead of us,” he said. “This near Summertide, that’s more than enough to kill them all.”