When the rover began tilting upwards, Andrew knew that they'd finally begun climbing the slopes of Etna Mons.

     Andrew took a moment to make sure Windsor and Fox were comfortable and safe, then returned to the cockpit to see how things were going. The warmth of the volcano meant that there was no ice here. There was only bare rock visible through the cockpit window. Scattered with boulders, but loose and crumbly enough that the wheels were able to get a good grip on it. Here and there he also saw the frozen remains of grass and small shrubs, withered and black. The land ahead looked flat. Only the tilt of the rover told him that they were climbing. They were too close to the volcano for it to look like a volcano. It looked more as if they were climbing the side of a moderately steep valley.

     Andrew's heart quailed to see the other rover close ahead of them, bouncing and shuddering as it drove across the uneven ground. Occasionally its motion slowed as its wheels lost their grip, throwing rocks and loose soil backwards as they spun. Other times it surged ahead as it passed over a region of compact but uneven ground. Their own rover also surged and slowed, with the result that the gap between the two rovers opened and closed erratically. Nevertheless the gap was slowly narrowing as Cheval used his manual control over the rover to take them over the best ground.

     "Best get suited up," the Sergeant told him. "We can't be more than half an hour from the caldera."

     "Right," said Andrew, his mouth dry. He turned to leave, but paused as something new entered the oval of light cast by the headlights.

     It was a human corpse wrapped in thick layers of furs, his outline visible in the rocky snow that covered him like an extra blanket placed over him by a grieving and remorseful God. More followed, some sitting cross legged on the ground as if they'd sat down to die. The last of their food gone, the last stick of wood burned. He saw a family group. Father, mother and two small children, huddled together. Frozen forever in a last tender embrace. And then there were tents. A small city of them forming hundreds of mounds under the sooty grey, silicate snow.

     "The Etna refuge," said Cheval sadly. "They thought the heat of the volcano would give them a little extra time."

     "When you've got a family, I suppose you'll grasp at any straw," said Andrew. "I might have brought my own family here myself, if we'd been around at the time. Who knows what miracle might occur if you can just hang on a couple of days longer? A spokesman from one of the underground cities, maybe, saying come with us. We've got room for you after all... Watch out!"

     The rover drove straight over one of the tents, crushing it under its wheels. Ahead, they saw Fox's rover driving over others. A tent was caught on the jagged end of a bent and broken wheel cleat. As it was lifted away they saw two mummified corpses smashed into pieces like elaborate ice sculptures. Andrew reacted with horror. "Can't we go around?" he cried. "This is a desecration! This place should be preserved out of respect for the people who died here."

     "Perhaps you can use your sense of outrage to stop Fox's rover. If you can't, we have to go where it goes."

     Andrew stared at him helplessly, knowing he was right, but it didn't help. Off to the right, on a relatively level stretch of ground, he saw a larger tent the size of a circus ring that had a crucifix rising above it. He imagined it packed with the frozen corpses of those who had begged God to save them. Beside it was a small group of ambulances. He wondered what help they thought they'd be able to provide as the planet receded from the sun and the world froze. He stared at one scene of tragedy after another until he felt a kind of mental numbness coming over him. There was only so much tragedy the human mind could take, it seemed, before safety mechanisms kicked in to keep you from feeling any more.

     "Time to get suited up," repeated Cheval. "Quick, while we've still got time."

     Andrew looked across at him, wondering how he was able to remain so unaffected by what he was seeing all around him. Perhaps he was feeling the same as Andrew and was just better at hiding it. He was glad to leave the cockpit, though. Away from the sight of what they were driving over.

     He paused for a moment in the living room to check on Fox and Windsor. "You're wasting your time," said the historian, staring at him with a broad grin. He looked half an inch from death, but seemed to gain new strength from the opportunity to mock his captors. "I disabled the controls. You can't take it off autopilot and you can't reprogram the autopilot. Even if you get aboard, you can't stop it going where I told it to go."

     "He's lying," said Windsor, who was still lying face down over the back of his chair to protect his back. "He wouldn't bother saying it if it was the truth. He'd just let us waste our efforts."

     "I'm warning you because I don't want you to endanger your life needlessly," Fox said to Andrew, though. "Everything I've done I did to save lives. You can't stop my rover. Just accept that."

     "Don't listen, Andrew," said Cheval over the intercom. "He's trying to delay you. Get going."

     Andrew nodded to himself and left, making his way to the outfitting room where he pulled off his coveralls and underwear and began getting into his surface suit. He tried not to think about what he was about to do. So long as all he was doing was putting on a suit he could fool his brain into thinking he was just going out for a walk, something he'd done a hundred times before.

     "Andrew," said Cheval over the intercom. "Get up top. We're drawing level with Fox's rover."

     "Right," replied Andrew. "On my way. No problem. No problem at all."

     He entered the airlock, closed the door behind him and opened the outer door. He went up to the edge and looked out. The ground was passing by below at an alarming speed, illuminated by the lights under the door. He saw rocks the size of ovens rolling past after having been knocked by the huge wheels. He also saw scraps of clothing, collapsed tents and pieces of human bodies, their exposed breaks shining like polished glass. The severed head of a young girl rolled by, coming to rest staring up at him. He wondered what her last thoughts had been. He wondered whether his own corpse would soon be lying there, among all the victims of The Freeze. He wondered whether anyone else would ever come this way and find him.

     He was thinking too much, he realised. The trick, he thought, was to turn his brain off, to put himself on autopilot. Let his body do what it needed to do without being distracted by an overactive imagination. That was easier said than done, though, as he found out when the rover went over a particularly large bump that almost threw him out the door. He clung to the edge of the door for sweet life until he'd managed ro regain his balance, his breath coming in fast, shallow gulps.

     "Andrew!" came Cheval's voice in his ears. "Are you up there yet? We're almost at the top."

     "On my way," said Andrew, struggling to keep his voice calm and even. "I'm fine."

     Making sure he had a firm grip he leaned out the door, looking to the side. The radiator fins needed occasional adjustment and maintenance so there was a set of rungs running up the side of the rover, just beside the airlock. They had never been meant to be used while the rover was in motion, though, and were just a little too far away to be within easy reach. To reach them, he had to hang out the door and reach as far as his outstretched fingers would go.

     He closed his eyes, took a moment to gather his courage and reached. His fingers brushed against hard, round steel, then fell away. On his second attempt he was able to get a grip, but to get onto the ladder properly he would have to launch himself out of the airlock and trust his hand to be able to hold on. If he failed, he would fall two metres onto hard rock moving past as twenty kilometres an hour. He might break a leg. He might rupture his suit. He might hit his head on a rock and be knocked unconscious to freeze to death as he lay on the cold ground.

     He remembered all the times he'd cursed himself for being a coward. How bad it had made him feel. He remembered how good it had felt when he'd helped Cheval deactivate the sentry weapon. He decided he preferred feeling good to feeling bad and so he tightened his grip on the handhold and let himself fall.

     He swung to the left and his outstretched left foot landed on a rung, which he put his weight on with a gasp of relief. He used it to push himself up and grab hold of the ladder with his other hand. Then he began climbing. He reached the top and pulled himself up onto the roof, grabbing hold of the nearest radiator fin to help him. The rover bumped and swayed under him like a wild horse trying to throw him off.

     The roof was textured to help people keep their footing but he remained on his hands and knees as he made his way to the edge of the rover, making sure to always have one hand securely grasping hold of the nearest radiator fin. Grains of silicate snow fell all around him like a steady rainfall, massaging his back as they hit his suit. The grains were rough and clumped together forming a compacted crust under his hands and knees. He imagined them tearing at the fabric of his suit, damaging it, wearing away the outer layers until he sprang an air leak. He put the thought firmly out of his head.

     He was forced to rise to his feet when the cold became too much for his knees. The radiator fins meant that the roof of the rover was warmer than the ground they were driving over, but he'd still get frostbite if he remained in contact with it for too long. As luck would have it, the rover chose that moment to drive over a particularly large rock and was thrown sharply to the right. Andrew had to cling grimly to the fins to avoid being thrown off.

     He reached the side of the rover and saw that Fox's rover was right alongside. So close that the two vehicles were bumping together with every ridge and hollow they drove over. If they'd been stationary he could have simply walked across. To do so, though, he would have to let go of the radiator fins, which his brain insisted would be suicidal at their present speed. He hesitated, therefore, and a gap opened up between the two rovers. A gap that widened until there were five or six metres between them. Andrew felt a mingled relief and horror. The gap was impossible. He'd have to wait until it narrowed again, and while he was waiting he looked around.

     Everything he knew about volcanos came from a single lesson in high school and the movies he'd watched while growing up. He'd expected the caldera to be a sharp edged crater with a sharp drop on the inside going down to a bubbling lake of lava. The reality was quite different. The summit of Etna Mons was wide and flat with several overlapping craters, most of which were filled with solid rock. The two rovers were driving across one such crater even now. Ahead of them, though, he saw a crater containing a fountain of red lava. Fox's rover turned to aim straight for it, driven by the instructions Fox had given it before he left. His own rover turned to follow it. They had less than a minute before they reached it.

     As the two rovers turned they came close alongside each other again and Andrew jumped before his common sense could stop him. He hit the top of Fox's rover and skidded across it, his hand reaching desperately for the nearest radiator fin. He missed.

     He carried on sliding, screaming in terror, but the silicate snow covering the top of the rover was pushed up in front of his body. Together with the textured surface of the rover, it formed a solid ridge that stopped him dead just a few centimetres from the edge. He lay there for a moment, sobbing in relief, before realising that the edge he was close to was the rear edge. The rungs down to the airlock must be right below him. He turned, taking his head over the edge, and looked down. There was the topmost rung. He turned around until his waist was over the edge, his legs dangling. He felt with his feet until he was standing on the rung, and began to carefully lower himself.

     Getting into the airlock was the most dangerous part of the whole operation. The outer door was open, which was a bit of luck, but how was he going to get through it?

     "The ladder," said Cheval in his ear. His rover had pulled back, Andrew saw, and the Sergeant was watching him through the cockpit window. "Use the ladder."

     "I'm on the ladder," Andrew pointed out.

     "The other ladder. The one from the airlock down to the ground."

     Andrew cursed himself for a fool. The entire rover was raised a metre from the ground by the massive wheels. A ladder was deployed from the airlock to help people get in and out. There were two controls to deploy the ladder. One inside the airlock, the other on the outside, near the bottom of the door where it could be reached by a man standing on the surface. Andrew reached over with his leg and kicked it with the toe of his boot.

     The ladder unfolded into place and Andrew launched himself sideways onto it before the saner part of his brain could stop him. He missed the rung he'd been aiming for and fell, but he was able to grab a lower rung instead. His legs dragged along the rocky ground and he winced as he felt the cold penetrating his skin like a thousand tiny daggers. He pulled himself up, got his feet on the lowest rung of the ladder and scrambled up it, into the airlock.

     The inner door was also open, which shouldn't have been possible. Fox must have jimmied the controls and disabled the safety mechanisms, but why would he do that? He put the puzzle out of his mind and just thanked his luck as he ran through, into the rover.

     "You're almost at the crater," said Cheval in his ear. "You've got seconds."

     Andrew ran. Through the outfitting room, down the corridor that ran beside the kitchen and the living room and into the cockpit. He landed heavily in the pilot's seat and slammed his hand hard on the autopilot switch, at the same time grabbing the joystick with his other hand and yanking it hard to the right.

     Nothing happened. The rover continued trundling on towards the roiling, boiling lake of lava he could see through the cockpit window. He thumped the autopilot switch again. The light above it continued to glow, indicating that the autopilot was still engaged. "He was telling the truth!" he yelled. "I can't stop the rover."

     "Then get out!" shouted back Cheval. "Get out! Now!"

     "I can disconnect the transformer in the service level," said Andrew. "Without power the rover will stop."

     "No time!" shouted back the Sergeant. "You're in the lava."

     The rover's nose was tipping downwards. He jumped out of the seat, but it was now an uphill climb to the door as the front end of the rover began to sink. He turned and saw fragments of semi-solid lava thrown up in front of the window as the rover ploughed into it. He dropped onto hands and feet and climbed back the way he'd come, dodging a fire extinguisher as it fell past him and through the cockpit door.

     The rover began to level off, telling him that the front wheels had touched bottom. He reached the airlock and saw nothing but starry sky through the outer door. There was no way of telling if there was lava or solid rock below it so he just ran through and jumped with all his might.

     He landed on solid rock that vibrated with the energies of the volcano. He rolled and scrambled back to his feet before the cold rock could injure him, only realising when he was standing again that the rock was warm. Hot, even. Warmed by the heat of the lava, so close alongside. Silicate snow was falling all around, making it hard to see more than a few dozen metres, but he could see Fox's rover, still driving forward, its wheels dripping with lava that looked like red treacle.

     A warning light appeared in his visor's head up display warning him that the suit was overheating. He took a few steps back, but couldn't take his eyes from Fox's rover which was now low enough that lava was flowing in through the open airlock doors. The doors that Fox had deliberately left open to keep the rover from just floating on lava that wasn't hot enough to melt steel. He felt an additional vibration in the rocks under his feet and looked around to see his own rover coming up alongside him. "I failed," he muttered to himself. "I failed."

     "We all failed," he heard Windsor saying. In the background he could hear Fox laughing.

     Cheval said nothing, and Andrew could think of nothing else to say. All he could do was stand and watch as Fox's rover continued forward, now swimming more than driving, like some ancient river boat with six paddle wheels. It settled lower as the lava continued to flood in until only the radiator fins could still be seen, now glowing red as they vainly tried to shed the heat. Then they also disappeared from view and the slag floating on the lava closed over the spot where it had been, leaving no sign that the rover had ever been there.

     Andrew stood there for a few minutes longer while something died inside him leaving an empty hole that somehow felt heavy, like a great block of stone. He'd dared to cross from one moving rover to another, an act he had thought he'd be too scared to attempt, but instead of triumph and pride he felt only a great sense of betrayal, as if the prize he'd earned had been denied him by some cruel and sadistic judge.

     Eventually, with nothing else to do, he turned and walked slowly back to his own rover. The rover in which Fox was still laughing with jubilation and triumph.