"Water is funny stuff," the Rememberer said. "Have you ever heard of hot ice?"

Rhoda had her engineering officers extrapolate what had happened, from the hints in Hume's account.

Ice formed naturally when heat was extracted from a body of water, the hydrogen-oxygen molecules settling into a s.p.a.ce-filling solid lattice. But the Squeem had discovered that you can create a particular kind of ice, called polar cubic ice, even at high temperatures, with electricity.

"We know about this too," Reg Kaser said. "All you have to do is pa.s.s an electric field through the water a strong one, a million volts a meter. The two hydrogen atoms in a water molecule have a slight positive charge, and the oxygen atom a negative one, so the electric field makes the molecules line up like fence posts. And there you have it, ice, at as high a temperature as you like. This happens in nature, though on a microscopic scale, wherever there are strong enough electric fields. Such as across the membranes of nerve cells, or in the cavities of proteins. Mini-icebergs riding around inside your cells. Amazing."

Hume said, "The Squeem were masters of this sort of technology. Masters of water!' water!'

"And so," Rhoda prompted, "on occupied Earth "

"They froze the water."

"What water?"

"All of it."

Earth's oceans plated over with ice, right down to the equator, and then froze to their beds. And then the hard whiteness crept up the river valleys.

Harry and his codissidents were made to watch, on vast softscreens. Indeed, the Squeem made everybody watch, everybody capable of understanding.

"Even the aquifers froze. Even the moisture in the ground," Hume whispered. "Everybody walked around on permafrost, down to the equator.

"The Squeem controlled it, somehow. After all, humans are just big bags of water. We didn't freeze, nor did the gra.s.ses, the animals, the birds, the moisture in the air. Of course, rainfall was screwed, because nothing was evaporating from the oceans.

"They kept it up for a full year. By then, people were dying of the drought and the cold. And Earth blazed white, a symbol of the Squeem's dominance, visible even to all the off-planet refugees and hideouts, visible light-years away.

"Then they released the field. There was a lot of damage as all that ice went away. Coastlines shattered, river valleys gouged out, melt.w.a.ter floods, climatic horrors. Lots of people died, as usual.

"And the oceans were left sterile. Oh, the Squeem allowed gradual restocking, from samples in climate-crash gene-store facilities, that kind of thing. The oceans didn't stay dead. But still, what followed would always be artificial. The link with the deepest past of life on Earth was cut.

"It was the worst act the Squeem, an aquatic species, could think of," Hume said. "To murder oceans. They thought it would crush human resistance once and for all. And it worked. But not for the reasons they imagined."

"When it was done, they just let Harry and his colleagues go. Harry came out of that prison camp near Thunder Bay, and found himself in an aftermath society.

"It had been by far the worst act of terror ever inflicted on the Earth, by mankind or anybody else.

"And it had cut through some deep umbilical connection we still evidently had with the mother oceans. We came from the oceans. Our deepest cellular origins lie there. When hominids arose, even before we were intelligent, we used the water, river courses and ocean sh.o.r.es, as roadways as we covered the planet. Now all that was gone. Everybody just wandered around stunned."

"I'm not surprised," said Rhoda. She a.s.sessed the reactions of her crew to this forgotten crime. Anger, shock, a l.u.s.t for revenge.

"And," Hume said now, "the Squeem became concerned. A large proportion of mankind was plagued by flashbacks, crippling fear. Productivity was dropping. Birth rates falling. They didn't want to kill off their cheap labor. Maybe they saw they'd gone too far.

"World leaders were summoned to a kind of summit. I say leaders. After two decades of the Squeem, there were no presidents, no UN secretary-general. The 'leaders' were labor organizers, necessary academics like doctors, a few religious types.

"And the Squeem offered, not a restoration, for what they had done could not be put right, but a kind of cure."

Most of humanity was suffering from a deep kind of post-traumatic stress disorder.

The memories of the freezing were etched deeply into every human brain. Like all traumas, the event had produced a rush of adrenaline and noradrenaline, which then forced a brain center called the amygdala to imprint the memories into the hippocampus, the memory center, very deeply. It was essentially a survival mechanism, so that any reminder of the event triggered deep memories and a fast response.

Sometimes such memories were gradually extinguished, the memory pathways overridden if not erased. But in this case, for the majority of man-kind, the extinguishing mechanism didn't work well. The event had been too huge, too deep. And global post-trauma stress was the result.

But this could be rectified.

"There are ways to control memory formation," Reg Kaser murmured to Rhoda, taking another briefing from his data slate. "Drugs like beta blockers that inhibit the action of adrenaline and noradrenaline, and so reduce their memory-forming capabilities. A stress-related hormone called cortisol can inhibit memory retrieval. There are drugs that release a brain chemical called glutamate that enhances learning, thereby accelerating the normal memory extinguishing process. And so on."

"You're talking about altering memories with drugs," Rhoda murmured.

"Since the twentieth century, when neuroscience was established as a discipline, human societies have always shied away from memory-changing technology," Kaser said. "There are obvious ethical issues. A memory is part of your ident.i.ty, after all. Does anybody else have the right to take away part of you? you? And suppose a criminal deliberately erases all her own memory of her crime. If she doesn't remember it, is she any longer responsible? That was used as a defense in a criminal trial during " And suppose a criminal deliberately erases all her own memory of her crime. If she doesn't remember it, is she any longer responsible? That was used as a defense in a criminal trial during "

"Never mind," Rhoda said.

"The point is, such technologies have existed in the past. And after a couple of decades of occupation, the Squeem, presumably with human collaborators, were able to come up with a suitable treatment."

"Yes. And this is what they offered us," Hume said. "An engineered virus that would spread through mankind, across the Earth. Eventually moles would carry it through the off-planet populations too. It wouldn't be comfortable. You would have a nightmare, reliving the trauma one last time. But that would make the memory labile again for a short time. And so it could be treated."

"They would delete the memory of the freezing, of this vast crime," Rhoda said. "From everybody's heads."

"That was the idea. There would have to be a subsidiary activity of removing it from various records, but there weren't too many marine biologists at the height of the occupation. It wouldn't be difficult.

"This solution served the Squeem's goals, you see. People would stay pliable. They just wouldn't know why."

Kaser said sharply, "And, since none of us have heard of this freezing before, I take it that these 'leaders' made this supine choice on behalf of the rest of mankind."

"You shouldn't judge them," Hume said. "We had been enslaved from s.p.a.ce, for decades already. They could see no way out. The only choice was between a future of terrified subjugation, or a calmer one vague, baffled, adjusted.

"Even Harry Gage and his resistance colleagues knew they were beaten. They submitted. But," he said, and a smile spread over his leathery face, "there was one last act of defiance."

Everybody alive would forget the terror. Everybody but one.

"It wasn't sophisticated. They would just hide one person away, for a year, perhaps more. Earth's a big planet. There were plenty of places to hide. And not all the biochemists had gone over to the Squeem. Some of them helped out with screens against the virus. And when he or she came out of her hole in the ground "

Rhoda guessed, "Harry Gage was the first Rememberer."

Hume smiled. "They chose him by lot. It could have been anyone. It's the only reason we remember Harry now, the only extraordinary thing that happened in his life.

"He went into the hole without a word of protest. And when he came back out, he found himself the only one who remembered the freezing. A kind of living memorial to a deleted past.

"Harry just went back to work. But the course of the rest of his life was set out. It must have been hard for him, hard not to talk about what he knew. It's been hard for me, me, and I didn't live through it. and I didn't live through it.

"Harry Gage died in his late forties. It wasn't an age when people grew old. But he fulfilled his last mission, which was to transmit his memories to another.

"The Second Rememberer was in her thirties when the Squeem regime began to crumble sooner than anybody had expected. She too died young. But she was able to pa.s.s on her knowledge to another in turn.

"And so it went. Two centuries after the Squeem conquered Earth, I am the Sixth Rememberer."

Rhoda nodded. "And you tried to recruit Lonnie Tekinene."

Hume sighed. "That was the idea. I left it a bit late in life to be befriending ten-year-olds."

"But," Reg Kaser said, "even though the Squeem fell so long ago, none of you thought to reveal the truth of all this oral history until now."

Hume shrugged. "When would have been right? Each of the Rememberers has had to make that judgment. It was only when I learned of your pocket of Squeem, after the pa.s.sage of two centuries, that I judged the time was right. You need to know the whole truth about the Squeem in order to deal with them." His face twisted. "But I wasn't sure. sure. I'm still not." I'm still not."

Rhoda said gently, "So how do you feel now?"

"Relieved. It's a burden, to be the only one who knows."

It took Rhoda Voynet and her crew another week of data-gathering before she felt ready to make her judgment.

She called Reg Kaser to her cabin, and fired up her percolator once more. Beyond her picture window, Saturn turned, its cloudy face impa.s.sive before the turmoil of living things.

"They've started to find proof," she said to Kaser.

"Of what?"

"The freezing. The geologists. The biologists, trawling the seabeds for crushed whale bones. My historian colleagues, finding traces of deleted records. Global evidence of a decade-long glaciation event. It was always there, but unnoticed; it just needed a framing hypothesis to fit it all together."

"So Hume was telling the truth."

"It seems so."

"Meanwhile," Kaser said, "I've been talking to the xenologists, who have been in contact with those Squeem down there under the ice. The Squeem have been making their own case."

"About what?"

"About why we should be lenient. The Squeem say they suffered some deep trauma of their own. After all, they are aquatic, they're functionally fishlike, and it must have taken a huge disjunction to lift them out of their ocean and into s.p.a.ce." Kaser scrolled through notes on his slate. "Something about an invasion, by yet another world-conquering species. The Squeem managed to enslave the slavers, and started an empire of their own. Something on those lines. It's complicated."

Rhoda said harshly, "And that justifies them occupying Earth?"

"I suppose that's the argument. But you're the commanding officer."

"I am, aren't I?" She looked him straight in the eye. "I want to know my options. Tell me about the weapon. The one that will destroy the moon."

He looked away. "If you're sure this is need-to-know only."

"I need to know."

"It's not a human development," Kaser said. "Not even Squeem."

Rhoda glanced beyond Saturn's limb, at the stars. "Something hideous we've found. Out there."

"Yes."

Even under the oppressive Squeem occupation, humans had learned much.

They learned, for example, that much of the Squeem's high technology such as their hyperdrive was not indigenous. It was copied, sometimes at second or third hand, based on the designs of an older, more powerful species.

"It was during the occupation," Kaser said, "that the name 'Xeelee' entered human discourse. The primal source of all this good stuff."

Rhoda shuddered. "And is this new weapon a Xeelee artifact?"

"It may be. Stuff gets swapped around out there. Purloined. Modified. We don't know enough about the Xeelee to say."

"Tell me what this thing does."

"Maybe you know that the planet Jupiter is being destroyed. Eaten up from within by a swarm of black holes."

"Yes." In fact, Rhoda knew a little more about it than that.

"If we could make a black hole," Kaser said, "we could throw it at Rhea and demolish it the same way."

"We can't make a black hole."

"No. But we have a technology almost as good." He pulled up graphics on his slate and showed her. "It's a way to create a dark energy black hole."

"A what what?"

"It's all to do with quantum physics," he said.

"Oh, it would be..."

It was another kind of freezing, a phase transition. But this would happen at the quantum level. In a "quantum critical phase transition," ordinary matter congealed into a kind of superconductor, and then into a sluggish stuff in which even subatomic fluctuations died, and ma.s.s-energy was shed.

"It's as if time itself is freezing out," Kaser said. He mimed with his hands. "So you have a spherical sh.e.l.l. Just a volume in s.p.a.ce. You arrange for matter falling on its surface to go through this quantum phase transition. And as your infalling matter pa.s.ses into the interior, its ma.s.s is dumped, converted to vacuum energy. Dark energy."

"Why doesn't this sh.e.l.l implode?"

"Because dark energy has a repulsive effect. Antigravity. Dark energy is already the dominant component of the universe's ma.s.s-energy, and the antigravity force it produces will drive the expansion of the universe in the future. So I'm told by the physicists. Anyhow, the repulsion can balance the infall of matter."

"It can can balance." balance."

Kaser grinned. "That's the engineering challenge, I guess. If you get it right, you get a stable object which externally looks just like a black hole. Inside, there's no singularity, just a mush of dark energy, but any structure is destroyed just the same. These things are found in nature, apparently."

"And they are easier to make than genuine black holes?"

"So it seems. You do need a big box of exotic matter, that is negative-energy matter, to make it work." He kept grinning.

"Poole wormhole mouths."

"Just the job. The Squeem wrecked the old Poole wormhole transport system, but they left the wormhole mouths in place. There are several still orbiting Saturn. Any one of them will do."

"And if we throw one of these things into Rhea "

"It will eat up the moon."