The four rested a while longer, monitoring the airflow, exercising Sherkaner's scheme for controlling the exotherms. Unnerby and Amberdon Nizhnimor went through the detailed checklist, passing suspicious and broken items across to Sherkaner. Nizhnimor, Haven, and Unnerby were very bright people, a chemist and two engineers. But they were also combat professionals. Sherkaner found fascinating the change that came over them when they moved out of the lab and into the field. Unnerby especially was such a layering: hardbitten soldier atop imaginative engineer, hiding a traditional, straitlaced morality. Sherkaner had known the sergeant for seven years now. The fellow's initial contempt for Underhill schemes was long past; they had been close friends. But when their Team finally moved to the Eastern Front, his manner had become distant. He had begun to address Underhill as "sir," and sometimes his respectfulness was edged with impatience.

He'd asked Victory about that. It had been the last time they were alone together, in a cold burrow-barracks beneath the last operating aerodrome on the Eastern Front. She had laughed at the question. "Ah, dear soft one, what do you expect? Hrunk will have operational command once the Team leaves friendly territory.You are the civilian advisor with no military training, who must somehow be tucked into the chain of command. He needs your instant obedience, but also your imagination and flexibility." She laughed softly; only a curtain separated their conversation from the main hall of the narrow barracks. "If you were an ordinary recruit, Unnerby would have fried your shell half a dozen times by now. The poor cobber is so afraid that when seconds count, your genius will be caught on something completely irrelevant—astronomy, whatever."

"Um." Actually, he had wondered how the stars might look without the atmosphere to dim their colors. "I see what you mean. Put that way, I'm surprised he let Greenval put me on the Team."

"Are you kidding? Hrunk demanded you be on it. He knows there'll be surprises that only you can figure out. As I said; he's a cobber with a problem."

It wasn't often that Sherkaner Underhill felt taken aback, but this was one of those times. "Well, I'll be good."

"Yes, I know you will. I just wanted you to know what Hrunk is up against....Hey, you can look on it as a behavioral mystery: How can such radically crazy people cooperate and survive where no one has ever lived before?" Maybe she meant it as a joke, but itwas an interesting question.

• • •

Without doubt, their vehicle was the strangest in all history: part submarine, part portable deepness, part sludge bucket. Now the fifteen-foot shell rested in a shallow pool of glowing green and tepid-red. The water was in a vacuum boil, gases swirling up from it, chilling into tiny crystals, and falling back. Unnerby pushed open the hatch, and the team formed a chain, handing equipment and exotherm tanks from one to the next to the next, until the ground just beyond the pool was piled with the gear they would carry.

They strung audio cable between themselves, Underhill to Unnerby to Haven to Nizhnimor. Sherkaner had been hoping for portable radios almost until the end, but such gear was still too bulky and no one was sure how it would operate under these conditions. So they each could talk to just one other team member. Still, they needed safety lines in any case, so the cable was no extra inconvenience.

Sherkaner led the way back to the lakeshore, with Unnerby behind him, and Nizhnimor and Haven pulling the sled. Away from their submarine, the darkness closed in. There were still glimmers of heat-red light, where exotherms had sprayed across the ground; the sub had burned tons of fuel in melting its way to the surface. The rest of the mission must be powered by just the exotherms they could carry and what fuels they could find beneath the snow.

More than anything else, the exotherms were the trick that made this walk in the Dark possible. Before the invention of the microscope, the "great thinkers" claimed that what separated the higher animals from the rest of life was their ability to survive as individuals through the Great Dark. Plants and simpler animals died; it was only their encysted eggs that survived. Nowadays, it was known that many single-celled animals survived freezing just fine, and without having to retreat to deepnesses. Even stranger, and this had been discovered by biologists at Kingschool while Sherkaner was an undergraduate, there were forms of Lesser Bacteria that lived in volcanoes and stayed active right through the Dark. Sherkaner had been very taken by these microscopic creatures. The professors assumed that such creatures must suspend or sporulate when a volcano went cold, but he wondered if there might be varieties that could live through freezes by making their own heat. After all, even in the Dark, there was still plenty of oxygen—and in most places there was a layer of organic ruin beneath the airsnow. If there were some catalyst for starting oxidation at super-low temperatures, maybe the little bugs could just "burn" vegetation between volcanic surges. Such bacteria would be the best adapted of all to live after Dark.

In retrospect, it was mainly Sherkaner's ignorance that permitted him to entertain the idea. The two life strategies required entirely different chemistries. The external oxidation effect was very weak, and in warm environments nonexistent. In many situations, the trick was a serious disability to the little bugs; the two metabolisms were generally poisonous to each other. In the Dark, they would gain a very slight advantage if they were near a periodic volcanic hot spot. It would never have been noticed if Sherkaner hadn't gone looking for it. He had turned an undergraduate biology lab into a frozen swamp and gotten himself (temporarily) kicked out of school, but there they were: his exotherms.

After seven years of selective breeding by the Materials Research Department, the bacteria had a pure, high-velocity oxidizing metabolism. So when Sherkaner slopped exotherm sludge into the airsnow, there was a burst of vapor, and then a tiny glow that faded as the still-liquid droplet sank and cooled. A second would pass and if you looked very carefully (and if the exotherms in that droplet had been lucky) you would see a faint light frombeneath the snow, feeding across the surface of whatever buried organics there might be.

The glow was sprouting brighter now on his left. The airsnow shivered and slumped and some kind of steam curled out of it. Sherkaner tugged on the cable to Unnerby, guiding the team toward denser fuel. However clever the idea, using exotherms was still a form of firemaking. Airsnow was everywhere, but the combustibles were hidden. It was only the work of trillions of Lesser Bacteria that made it possible to find and use the fuel. For a while, even Materials Research had been intimidated by their creation. Like the mat algae on the Southern Banks, these tiny creatures were in a sense social. They moved and reproduced as fast as any mat that crawled the Banks. What if this excursion set the world on fire? But in fact the high-velocity metabolism was bacterial suicide. Underhill and company had at most fifteen hours before the last of their exotherms would all die.

Soon they were off the lake, and walking across a level field that had been the Base Commander's bowling green in the Waning Years. Fuel was plentiful here; at one point the exotherms got into a fallen mound of vegetation, the remains of a traumtree. The pile glowed more and more warmly, until a brilliant emerald light exploded through the snow. For a few moments, the field and the buildings beyond were clearly visible. Then the green light faded, and there was just the heat-red glow.