He was treading carefully here; masking his ignorance of Setterholm"s deeper motives by playing on the man"s vanity.

"Clever of me if I did."

"Oh, yes. I wouldn"t doubt that at all. And it must have driven you to distraction, that you could see what the others couldn"t. Naturally, you wanted to protect the worms, when you saw them under threat."

"Sorry, Nevil, but you"re going to have to try a lot harder than that." He paused and patted the machine"s matt-silver casing, clearly unable to pretend that he did not know what it was. "It"s radar, yes.

It can probe the interior of the glacier with sub-centimeter resolution, to a depth of several tens of meters."

"Which would be rather useful if you wanted to study the worms."

Setterholm shrugged. "I suppose so. A climatologist interested in glacial flow might also have use for the information."

"Like Iverson?" Clavain took a step closer to Setterholm and the radar equipment. He could see the display more clearly now: a fibrous tangle of mainly green lines slowly spinning in s.p.a.ce, with a denser structure traced out in red near its heart. "Like the man you killed?"

"I told you, I"m Iverson."

Clavain stepped toward him with the ice-pick held double-handed, but when he was a few meters from the man he veered past and made his way to the wall. Setterholm had flinched, but he had not seemed unduly worried that Clavain was about to try and hurt him.

"I"ll be frank with you," Clavain said, raising the pick. "I don"t really understand what it is about the worms."

"What are you going to do?"

"This."

Clavain smashed the pick against the wall as hard as he was able. It was enough: a layer of ice fractured noisily away, sliding down like a miniature avalanche to land in pieces at his feet; each fist-sized shard veined with worm trails.

"Stop," Setterholm said.

"Why? What do you care, if you"re not interested in the worms?"

Clavain smashed the ice again, dislodging another layer.

"You..." Setterholm paused. "You could bring the whole place down on us if you"re not careful."

Clavain raised the pick again, letting out a groan of effort as he swung. This time he put all his weight behind the swing; all his fury, and a chunk the size of his upper body calved noisily from the wall.

"I"ll take that risk," Clavain said.

"No. You"ve got to stop."

"Why? It"s only ice."

"No!"

Setterholm rushed him, knocking him to his feet. The icepick spun from his hand and the two of them crashed into the ground, Setterholm landing on his chest. He pressed his faceplate close to Clavain"s, every bead of sweat on his forehead gleaming like a precise little jewel.

"I told you to stop."

Clavain found it hard to speak with the pressure on his chest, but forced out the words with effort. "I think we can dispense with the charade that you"re Iverson now, can"t we?"

"You shouldn"t have harmed it."

"No... and neither should the others, eh? But they needed that ice very badly."

Now Setterholm"s voice held a tone of dull resignation. "The reactor, you mean?"

"Yes. The fusion plant." Clavain allowed himself to feel some small satisfaction, before adding:"Actually, it was Galiana who made the connection, not me. That the reactor ran on ice, I mean. And after all the outlying bases had been evacuated, they had to keep everyone alive back at the main one.

And that meant more load on the reactor. Which meant it needed more ice, of which there was hardly a shortage in the immediate vicinity."

"But they couldn"t be allowed to harvest the ice. Not after what I"d discovered."

Clavain nodded, observing that the reversion from Iverson to Setterholm was now complete.

"No. The ice was precious, wasn"t it. Infinitely more so than anyone else realized. Without that ice the worms would have died..."

"You don"t understand either, do you?"

Clavain swallowed. "I think I understand more than the others, Setterholm. You realized that the worms-"

"It wasn"t the d.a.m.ned worms!" He had shouted-Setterholm had turned on a loudspeaker function in his suit which Clavain had not located yet-and for a moment the words crashed around the great ice chamber, threatening to start the tiny chain reaction of fractures which would collapse the whole. But when silence had returned-disturbed only by the rasp of Clavain"s breathing-nothing had changed.

"It wasn"t the worms?"

"No." Setterholm was calmer now, as if the point had been made. "No-not really. They were important, yes-but as low-level elements in a much more complex system. Don"t you understand?"

Clavain strove for honesty. "I never really understood what it was that fascinated you about them.

They seemed quite simple to me."

Setterholm removed his weight from Clavain and rose up onto his feet again. "That"s because they are.

A child could grasp the biology of a single ice worm in an afternoon. Felka did, in fact. Oh, she"s wonderful, Nevil." Setterholm"s teeth flashed a smile that chilled Clavain. "The things she could unravel...

she isn"t a failure; not at all. I think she"s something miraculous we barely comprehend."

"Unlike the worms."

"Yes. They"re like clockwork toys; programmed with a few simple rules." Setterholm stooped down and grabbed the ice-pick for himself. "They always respond in exactly the same way to the same input stimulus. And the kinds of stimuli they respond to are simple in the extreme: a few gradations of temperature; a few biochemical cues picked up from the ice itself. But the emergent properties..."

Clavain forced himself to a sitting position. "There"s that word again."

"It"s the network, Nevil. The system of tunnels the worms dig through the ice. Don"t you understand?

That"s where the real complexity lies. That"s what I was always more interested in. Of course, it took me years to see it for what it was..."

"Which was?"

"A self-evolving network. One that has the capacity to adapt; to learn."

"It"s just a series of channels bored through ice, Setterholm."

"No. It"s infinitely more than that." The man craned his neck as far as the architecture of his suit would allow, reveling in the palatial beauty of the chamber. "There are two essential elements in any neural network, Nevil. Connections and nodes are necessary, but not enough. The connections must be capable of being weighted; adjusted in strength according to usefulness. And the nodes must be capable of processing the inputs from the connections in a deterministic manner, like logic gates." He gestured around the chamber. "Here, there is no absolutely sharp distinction between the connections and the nodes, but the essences remain. The worms lay down secretions when they travel, and those secretions determine how other worms make use of the same channels; whether they utilize one route or another.

There are many determining factors-the s.e.xes of the worms, the seasons; others I won"t bore you with.

But the point is simple. The secretions-and the effect they have on the worms-mean that the topology of the network is governed by subtle emergent principles. And the breeding tangles function as logic gates; processing the inputs from their connecting nodes according to the rules of worm s.e.x, caste and hierarchy. It"s messy, slow and biological-but the end result is that the worm colony as a whole functions as a neural network. It"s a program that the worms themselves are running, even though any given worm hasn"t a clue that it"s a part of a larger whole." Clavain absorbed all that and thought carefully before asking the question that occurred to him. "How does it change?"

"Slowly," Setterholm said. "Sometimes routes fall into disuse because the secretions inhibit other worms from using them. Gradually, the glacier seals them shut. At the same time other cracks open by chance-the glacier"s own fracturing imposes a constant chaotic background on the network-or the worms bore new holes. Seen in slow-motion-our time frame-almost nothing ever seems to happen, let alone change. But imagine speeding things up, Nevil. Imagine if we could see the way the network has changed over the last century, or the last thousand years... imagine what we might find. A constantly evolving loom of connections; shifting and changing eternally. Now. Does that remind you of anything?"

Clavain answered in the only way that he knew would satisfy Setterholm. "A mind, I suppose. A newborn one, still forging neural connections."

"Yes. Oh, you"d doubtless like to point out that the network is isolated, so it can"t be responding to stimuli beyond itself-but we can"t know that for certain. A season is like a heartbeat here, Nevil! What we think of as geologically slow processes-a glacier cracking; two glaciers colliding-those events could be as forceful as caresses and sounds to a blind child." He paused and glanced at the screen in the back of the imaging radar. "That"s what I wanted to find out. A century ago, I was able to study the network for a handful of decades. And I found something that astonished me. The colony moves; reshapes itself constantly, as the glacier shifts and breaks up. But no matter how radically the network changes its periphery; no matter how thoroughly the loom evolves, there are deep structures inside the network that are always preserved." Setterholm"s finger traced the red ma.s.s at the heart of the green tunnel map. "In the language of network topology, the tunnel system is scale-free rather than exponential.

It"s the hallmark of a highly organized network with a few rather specialized processing centers-hubs, if you like. This is one. I believe its function is to cause the whole network to move away from a widening fracture in the glacier. It would take me much more than a century to know for sure, although everything I"ve seen here confirms what I thought originally. I mapped other structures in other colonies, too. They can be huge; spread across cubic kilometers of ice. But they always persist. Don"t you see what that means? The network has begun to develop specialized areas of function. It"s begun to process information, Nevil. It"s begun to creep its way toward thought."

Clavain looked around him once more, trying to see the chamber in the new light that Setterholm had revealed. Think not of the worms as ent.i.ties in their own right, he thought, but as electrical signals, ghosting along synaptic pathways in a neural network made of solid ice...

He shivered. It was the only appropriate response.

"Even if the network processes information ... there"s no reason to think it could ever become conscious."

"Why, Nevil? What"s the fundamental difference between perceiving the universe via electrical signals transmitted along nerve tissue, and via fracture patterns moving through a vast block of ice?"

"I suppose you have a point."

"I had to save them, Nevil. Not just the worms, but the network they were a part of. We couldn"t come all this way and just wipe out the first thinking thing we"d ever encountered in the universe, just because it didn"t fit into our neat little preconceived notions of what alien thought would actually be like."

"But saving the worms meant killing everyone else."

"You think I didn"t realize that? You think it didn"t agonize me to do what I had to do? I"m a human being, Nevil-not a monster. I knew exactly what I was doing and I knew exactly what it would make me look like to anyone who came here afterward."

"But you still did it."

"Put yourself in my shoes. How would you have acted?"

Clavain opened his mouth, expecting an answer to spring to mind. But nothing came; not for several seconds. He was thinking about Setterholm"s question, more thoroughly than he had done so far. Until then he had satisfied himself with the quiet, unquestioned a.s.sumption that he would not have acted the way Setterholm had done. But could he really be so sure? Setterholm, after all, had truly believed that the network formed a sentient whole; a thinking being. Possessing that knowledge must have made him feeldivinely chosen; sanctioned to commit any act to preserve the fabulously rare thing he had found. And he had, after all, been right.

"You haven"t answered me."

"That"s because I thought the question warranted something more than a flippant answer, Setterholm. I like to think I wouldn"t have acted the way you did, but I don"t suppose I can ever be sure of that."

Clavain stood up, inspecting his suit for damage; relieved that the scuffle had not injured him.

"You"ll never know."

"No. I never will. But one thing"s clear enough. I"ve heard you talk; heard the fire in your words. You believe in your network, and yet you still couldn"t make the others see it. I doubt I"d have been able to do much better, and I doubt that I"d have thought of a better way to preserve what you"d found."

"Then you"d have killed everyone, just like I did?"

The realization of it was like a hard burden someone had just placed on his shoulders. It was so much easier to feel incapable of such acts. But Clavain had been a soldier. He had killed more people than he could remember, even though those days had been a long time ago. It was really a lot less difficult to do, when you had a cause to believe in.

And Setterholm had definitely had a cause.

"Perhaps," Clavain said. "Perhaps I might have, yes."

He heard Setterholm sigh. "I"m glad. For a moment there..."

"For a moment what?"

"When you showed up with that pick, I thought you were planning to kill me." Setterholm hefted the pick, much as Clavain had done earlier. "You wouldn"t have done that, would you? I don"t deny that what I did was regrettable, but I had to do it."

"I understand."

"But what happens to me now? I can stay with you all, can"t I?"

"We probably won"t be staying on Diadem, I"m afraid. And I don"t think you"d really want to come with us; not if you knew what we"re really like."

"You can"t leave me alone here, not again."

"Why not? You"ll have your worms. And you can always kill yourself again and see who shows up next." Clavain turned to leave.

"No. You can"t go now."

"I"ll leave your rover on the surface. Maybe there are some supplies in it. Just don"t come anywhere near the base again. You won"t find a welcome there."

"I"ll die out here," Setterholm said.

"Start getting used to it."

He heard Setterholm"s feet scuffing across the ice; a walk breaking into a run. Clavain turned around calmly, unsurprised to see Setterholm coming toward him with the pick raised high, as a weapon.

Clavain sighed.

He reached into Setterholm"s skull; addressing the webs of machines which still floated in the man"s head, and instructed them to execute their host in a sudden, painless orgy of neural deconstruction. It was not a trick he could have done an hour ago, but after Galiana had planted the method in his mind, it was easy as sneezing. For a moment he understood what it must feel like to be a G.o.d.

And in that same moment Setterholm dropped the icepick, and stumbled, falling forward onto one end of the pick"s blade. It pierced his faceplate, but by then he was dead anyway.

"What I said was the truth," Clavain said. "I might have killed them as well, just like I said. I don"t like to think so, but I can"t say it isn"t in me. No; I don"t blame you for that; not at all."

With his boot he began to kick a dusting of frost over the dead man"s body. It would be too much bother to remove Setterholm from this place, and the machines inside him would sterilize his body, ensuring that none of his cells ever contaminated the glacier. And, as Clavain had told himself only a few days earlier, there were worse places to die than here. Or worse places to be left for dead, anyway.

When he was done; when what remained of Setterholm was just an ice-covered mound in the middle of a cavern, Clavain addressed him for one final time. "But that doesn"t make it right, either. It was still murder, Setterholm." He kicked a final divot of ice over the corpse. "Someone had to pay for it."

Undone