Cilia-of-Gold took herself off, away from the Chimney. She prowled the edge of the Ice cavern, feeding fitfully.

She was a hero. But she couldn’t bear the attention of others: their praise, the warmth of their bodies. All she seemed to desire now was the uncomplicated, silent coolness of Ice.

She brooded on the infestation that was spreading through her.

Seekers were a mystery. Nobody knew why Seekers compelled their hosts to isolate themselves, to bury themselves in the Ice. What was the point? When the hosts were destroyed, so were the Seekers.

Perhaps it wasn’t the Ice itself the Seekers desired, she wondered. Perhaps they sought, in their blind way, something beyond the Ice…

But there was nothing above the Ice. The caverns were hollows in an infinite, eternal Universe of Ice. Cilia-of-Gold, with a shudder, imagined herself burrowing, chewing her way into the endless Ice, upwards without limit… Was that, finally, how her life would end?

She hated the Seeker within her. She hated her body, for betraying her in this way; and she hated herself.

“Cilia-of-Gold.”

She turned, startled, and closed her carapace around herself reflexively.

It was Strong-Flukes and Ice-Born, together. Seeing their warm, familiar bodies, here in this desolate corner of the cavern, Cilia-of-Gold’s loneliness welled up inside her, like a Chimney of emotion.

But she swam away from her Three-mates, backwards, her carapace scraping on the cavern’s Ice wall.

Ice-Born came towards her, hesitantly. “We’re concerned about you.”

“Then don’t be,” she snapped. “Go back to the Chimney, and leave me here.”

“No,” Strong-Flukes said quietly.

Cilia-of-Gold felt desperate, angry, confined. “You know what’s wrong with me, Strong-Flukes. I have a Seeker. It’s going to kill me. And there’s nothing any of us can do about it.”

Their bodies pressed close around her now; she longed to open up her carapace to them and bury herself in their warmth.

“We know we’re going to lose you, Cilia-of-Gold,” Ice-Born said. It sounded as if she could barely speak. Ice-Born had always been the softest, the most loving, of the Three, Cilia-of-Gold thought, the warm heart of their relationship. “And—”

“Yes?”

Strong-Flukes opened her carapace wide. “We want to be Three again,” she said.

Already, Cilia-of-Gold saw with a surge of love and excitement, Strong-Flukes’s ovipositor was distended: swollen with one of the three isogametes which would fuse to form a new child, their fourth…

A child Cilia-of-Gold could never see growing to consciousness.

“No!” Her cilia pulsed with the single, agonized word.

Suddenly the warmth of her Three-mates was confining, claustrophobic. She had to get away from this prison of flesh; her mind was filled with visions of the coolness and purity of Ice: of clean, high Ice.

“Cilia-of-Gold. Wait. Please—”

She flung herself away, along the wall. She came to a tunnel mouth, and she plunged into it, relishing the tunnel’s cold, stagnant water.

“Cilia-of-Gold! Cilia-of-Gold!”

She hurled her body through the web of tunnels, carelessly colliding with walls of Ice so hard that she could feel her carapace splinter. On and on she swam, until the voices of her Three-mates were lost forever.

We’ve dug out a large part of the artifact, Irina, Dolores Wu reported. It’s a mass of what looks like hull material.

“Did you get a sample?”

No. We don’t have anything that could cut through material so dense… Irina, we’re looking at something beyond our understanding.

Larionova sighed. “Just tell me, Dolores,” she told Wu’s data-desk image.

Irina, we think we’re dealing with the Pauli Principle.

Pauli’s Exclusion Principle stated that no two fermions — electrons or quarks — could exist in the same quantum state. Only a certain number of electrons, for example, could share a given energy level in an atom. Adding more electrons caused complex shells of charge to build up around the atom’s nucleus. It was the electron shells — this consequence of Pauli — that gave the atom its chemical properties.

But the Pauli Principle didn’t apply to photons; it was possible for many photons to share the same quantum state. That was the essence of the laser: billions of photons, coherent, sharing the same quantum properties.

Irina, Wu said slowly, what would happen if you could turn off the Exclusion Principle, for a piece of fermionic matter?

“You can’t,” Larionova said immediately.

Of course not. Try to imagine anyway.

Larionova frowned. What if one could lase mass? “The atomic electron shells would implode, of course.”

Yes.

“All electrons would fall into their ground state. Chemistry would be impossible.”

Yes. But you may not care…

“Molecules would collapse. Atoms would fall into each other, releasing immense quantities of binding energy.”

You’d end up with a super dense substance, wouldn’t you? Completely non-reactive, chemically. And almost unbreachable, given the huge energies required to detach non-Pauli atoms.

Ideal hull material, Irina…

“But it’s all impossible,” Larionova said weakly. “You can’t violate Pauli.”

Of course you can’t, Dolores Wu replied.

Inside an opaqued bubble-shelter, Larionova, Dixon and Scholes sat on fold-out chairs, cradling coffees.

“If your mercuric was so smart,” Larionova said to Dixon, “how come he got himself stuck in the ice?”

Dixon shrugged. “In fact it goes deeper than that. It looked to us as if the mercuric burrowed his way up into the ice, deliberately. What kind of evolutionary advantage could there be in behavior like that? The mercuric was certain to be killed.”

“Yes,” Larionova said. She massaged her temples, thinking about the mercuric’s infection. “But maybe that thread-parasite had something to do with it. I mean, some parasites change the way their hosts behave.”

Scholes tapped at a data desk; text and images, reflected from the desk, flickered over his face. “That’s true. There are parasites which transfer themselves from one host to another — by forcing a primary host to get itself eaten by the second.”

Dixon’s wide face crumpled. “Lethe. That’s disgusting.”

“The lancet fluke,” Scholes read slowly, “is a parasite of some species of ant. The fluke can make its host climb to the top of a grass stem and then lock onto the stem with its mandibles — and wait until it’s swallowed by a grazing sheep. Then the fluke can go on to infest the sheep in turn.”

“Okay,” Dixon said. “But why would a parasite force its mercuric host to burrow up into the ice of a frozen ocean? When the host dies, the parasite dies, too. It doesn’t make sense.”

“There’s a lot about this that doesn’t make sense,” Larionova said. “Like, the whole question of the existence of life in the cavities in the first place. There’s no light down there. How do the mercurics survive, under two miles of ice?”

Scholes folded one leg on top of the other and scratched his ankle. “I’ve been going through the data desks.” He grimaced, self-deprecating. “A crash course in exotic biology. You want my theory?”

“Go ahead.”

“The thermal vents — which cause the cavities in the first place. The vents are the key. I think the bottom of the Chao ice-cap is like the mid-Atlantic ridge, back on Earth.

“The deep sea, a mile down, is a desert; by the time any particle of food has drifted down from the richer waters above it’s passed through so many guts that its energy content is exhausted.

“But along the Ridge, where tectonic plates are colliding, you have hydrothermal vents — just as at the bottom of Chao. And the heat from the Atlantic vents supports life: in little colonies, strung out along the mid-Atlantic Ridge. The vents form superheated fountains, smoking with deep-crust minerals which life can exploit: sulphides of copper, zinc, lead and iron, for instance. And there are very steep temperature differences, and so there are high energy gradients — another prerequisite for life.”