The bus arrived two hours later.
It was a much smaller kind of rover, intended for nothing more than the transport of people across the surface of the Earth. The cockpit was much the same, and there was a similar outfitting room and airlock at the back, but in between was nothing but rows of seats arranged in pairs on either side of a central aisle.
The tiny sun was just beginning to rise, making the summits of the surrounding hills shine brilliantly in the surrounding blackness, when Andrew saw the gleam of headlights at the end of the valley behind them. He watched the bus slowly crawl along the valley floor below, homing in on their transponder signal, and come to a stop when it was almost below them, at the bottom of the mountainslope. A few minutes later the bus's airlock door opened and three men in surface suits climbed carefully out. They went to the side of the bus, opened a hatch and took out a large chest. Two of them carried the chest between them as the three men began carefully climbing the side of the valley.
Reaching the hab-rover, they placed the chest in its cargo hold, then went around to the airlock. Andrew and his whole family was waiting in the outfitting room when the inner airlock door opened and the three men entered. They took off their helmets and the first man, about fifty and with dignified looking grey temples glared furiously at Andrew Birch. "Would you care to explain what you're doing just sitting here when you're supposed to be chasing Reginald Fox?" he demanded.
"And you are?" Andrew replied.
The man glared harder, then began removing the upper portion of his suit. "Sergeant Charles Cheval, New London Police. This is Constable Frank Windsor and Constable Ivan Kartoshka. We're here to requisition this hab-rover and use it to apprehend Reginald Fox, who is now seven hours ahead of us instead of just five. You were about to explain why."
"I wasn't willing to risk the safety of my family," Andrew replied stiffly. "We're parked on rock, at an inclinations of nineteen degrees from horizontal. When we move, we run the risk of slipping down the slope and maybe overturning. I wasn't willing to take that risk with my family aboard."
Cheval continued to glare at him, but then he looked at Susan and the children and his face softened a little. "Your family will suit up and go back to the city in the bus," he said. "You will stay aboard to assist us."
Andrew nodded and gave a nod to his family, who began stripping off their coveralls. Windsor, still removing his suit, took a moment to admire Susan's bare body. She ignored him. The Birch family then began putting on their surface suits while the three policemen put on the plain white standard issue coveralls that all rovers carried for the use of visitors. There were similar coveralls waiting in the bus for the Birch family when they got there.
"Be careful!" Susan said to Andrew, her helmet in her hand. "Don't try to be a hero. Let these guys take all the risks."
"I will, I promise." He put his arms around her and hugged her tightly. She hugged him back. "Just go back to the city by the most direct route. No diversions. Understand?"
"No diversions," Susan agreed. "We'll just follow the tracks they made, all the way back to New London."
"Good. Hopefully we'll catch Fox in a couple of days and we'll meet up again. We'll be back at the dig site in no time."
"We'd better be. Be careful. Understand?"
"Understood." He kissed her, then hugged her again. Then he turned to the children. "You be careful too. Understood?"
"You're the one doing the stupid, dangerous thing," James pointed out. "You be careful."
"I promise."
He hugged them all one at a time, then watched as they filed into the airlock. "Don't forget to feed Cagney and Lacey," said David, looking back just before crossing the threshold.
"They'll be fine, I promise," Andrew replied. "His pet gerbils," he said to the three policemen. "In a cage in their bedroom." Windsor smiled with amusement but Cheval just glowered silently.
The airlock door closed and there was a hiss as the air was allowed to slowly escape to fall as a light shower of snow at the base of the rover. Every so often someone would go out with an ice pick and a shovel to fill a bucket with frozen nitrogen and oxygen, to replace the air they lost every time they used the airlock, but there was no need to do that for a few days. They had plenty of air on board.
James was the first to descend, having done it once before and knowing the dangers, and he was able to guide the others safely down. They paused before the external camera for a moment, to wave goodbye to Andrew one last time. Then they began carefully descending the side of the valley, one cautious step at a time.
Andrew watched then anxiously on the cockpit monitor screen, not allowing himself to relax until they were safely inside the bus. He continued to watch as it made a long, wide turn in the flat valley floor and only allowed himself to relax when it was trundling back the way they'd come. A bus was considerably faster than a hab-rover. They would be safely back in the city within six hours, back in the cramped apartment they'd lived in before taking out a mortgage on the rover, assuming it was still unoccupied. Otherwise they'd be living in one of the communal dorms until Andrew returned.
"I assume our pursuit of the fugitive can now resume," said Cheval pointedly.
"Yes," said Andrew. "Of course."
He fed power to the electric motors that drove the wheels and the rover slowly inched forward. Andrew took it slowly, imagining the spiked, steel wheels slipping and sliding on the bare rock, and indeed the rover did lurch a couple of times, its rear end slipping a metre or so downslope before the unevenness of the rock stopped it from going any further. Cheval, sitting in the co-pilot's chair, grimaced at their slow progress but said nothing, perhaps knowing full well how precarious their situation was. Eventually, though, they were back onto ice, the wheel cleats one again getting a firm grip on the ground beneath them, and Andrew breathed a sigh of relief.
"So," he said as he carefully descended the side of the valley to the tracks Reginald Fox's rover had left further down. "What was in that box you brought on board?"
"Guns," said Cheval simply.
Andrew's head jerked around, his eyes wide with alarm. "What? Guns? What the hell?"
"If Fox's been planning this from the beginning, there's no telling what he might have brought from the city," the Police Sergeant replied. "Weapons, explosives. We might need to defend ourselves."
"Where would he even get a gun?"
"There are illegal 3D printing templates for all kinds of things if you know who to ask and if you've got the money to pay for it. A smart man might even be able to design a gun from scratch. The gunpowder's the only really difficult thing to obtain, but even that can be cooked up in any decently equipped laboratory, such as the one you have at your dig site."
"People come and go from the lab all the time, he couldn't count on having a long enough period of solitude in which to do such a thing."
The Sergeant nodded. "I tend to agree, which is why I think it's more likely he brought weapons from the city. We have to be ready, just in case."
"Shit!" swore Andrew fervently. "I'm beginning to think my wife was right. I should have gone back to the city with her."
"Too late now," said Cheval with a wolfish smile. "You're deputised."
"I assume you haven't forgotten that we only have food for a few more days," Andrew added.
"Don't worry," said Cheval. "It's being taken care of."
☆☆☆
The Eden glacier was a much easier crossing than the Derwent glacier had been, with no geothermal heat to make it unstable. The surface was rough and uneven where the nitrogen ice was slowly flowing at a rate of inches a year, but the rover's superb suspension meant that the four occupants felt almost nothing as they trundled across it. Now and then the tracks left by Reginald Fox's rover doubled back on themselves where he'd come upon some impassable obstacle and been forced to find an alternate route and Cheval smiled with satisfaction as he imagined the time they were making up. By the time they were half way across he thought it very likely that they'd made up half the distance between themselves and their quarry. It wasn't impossible that they might catch him before they reached the pennines.
The Sergeant left the cockpit at around mid morning to answer a call of nature and Windsor came to replace him. "So," said the Constable as he sat in the co-pilot's chair. "Three children."
"Yep," replied Andrew, who knew what was coming.
"So that means..."
"Yep," said Andrew again.
"Which one? I'm guessing the youngest. Right? The one with the pale skin."
"David, right."
"Does he know?"
"Of course he does. We told him as soon as he was old enough to understand. The hardest part was when the other kids in his class found out. You know how cruel children can be. They would shout 'Fossil baby!' at him. Things like that. He dealt with it magnificently, though. Just ignored it, and after a while the other kids grew bored with it. They started treating him as just another kid. It helped that he wasn't the only one conceived in a test tube. There were two others in his class alone."
"It must be a good feeling," said Windsor. "Helping to keep The Promise."
Andrew nodded, although he almost never thought of it any more. David was just one of his children. As much his as either of the others.
"I've seen a lot of promise children around the city," Windsor added. "Always makes me think about the trust their biological parents must have had in us. I mean, for all they knew, we could have just taken their sacrifice and then forgotten about them. They were all dead. What would they know?"
"They knew we needed a lot more genetic diversity than fifty thousand people could provide," said Andrew. "Even with people of every race, every culture, we're going through a genetic bottleneck and that leaves us vulnerable to new pathogens. A new virus could crop up and wipe us all out because we don't have enough genetic diversity for some people to be immune. They didn't trust our morality. They trusted our self-interest. Our desire to ensure the continuity of the species."
"He looks like you," said Windsor. "Apart from being so white, of course."
"They try to match the child to the parent. Black children to darker skinned parents, asian children to parents with residual asian traits and so on. We're whiter than average, both me and Susan, so they chose him to be the surrogate child."
"How much does he know about them?"
"Quite a lot, I think. They left a whole digital dossier. Photographs, family histories and anecdotes. Enough to fill a book. He said he read it, but I don't think he's really interested. They're just people out of ancient history to him. He thinks of us as his parents." There was pride in his voice as he said this. He loved David as much as he loved his other children and it was a joy to know that the boy loved him back.
Then a beep came from the instrument panel and Andrew looked to see that a message had appeared on one of the monitor screens. "Our resupply almost here," he said.
"Good," said Windsor rising from his seat. "I'll go tell the Sergeant."
Andrew nodded as he gave the command for the rover to stop.
☆☆☆
The rocket shot across the sky like a meteor, travelling backwards. Its engines were firing, slowing it, and as it slowed its horizontal motion slowly changed to vertical motion until it was moving directly downward, towards a spot a few hundred metres from the rover.
Andrew Birch and Sergeant Cheval were sitting in the cockpit, watching as the rocket slowly descended until it was hovering a couple of hundred metres above the ground. Where its hot exhaust touched the ground the nitrogen ice was instantly vaporised, streams of matter shooting upwards like magma from an erupting volcano, only to fall around the rapidly growing crater as a shower of ice crystals that shattered as they hit the ground.
The rocket's upper stage, an ugly, lumpy block of aluminium, then separated and climbed upwards, propelled by its own small rocket motor. The rest of the rocket then began to climb again, its vertical motion changing to horizontal as it climbed until it was speeding back the way it had come, to the spaceport that had been built a few kilometres from New London.
The upper stage containing the payload doubled in size as the cushions surrounding it inflated with helium, the only substance known to man capable of existing as a gas at such a low temperature. The payload hit the surface of the glacier and bounced, spinning as it rose back into the black sky. It bounced again and again until it was rolling along the ground, eventually to settle in a depression between two compression ridges about five hundred metres from the rover. The cushions deflated and fell away revealing a bright orange canister blinking with bright red lights.
Andrew drove the rover towards it until he was parked alongside, and then Windsor and Kartoshka climbed out of the airlock to go retrieve it. They opened the outer casing and pulled out the cargo canister that was sitting inside. They picked it up between them and carried it back to put it in one of the rover's cargo holds where it would be surrounded by hot air until it was warm enough to be handled. Then its contents would be unpacked and taken to the kitchen.
"Enough food to last the four of us for six months," said Cheval with satisfaction. "There's nothing to stop us now. We can chase him to the ends of the Earth."
"If it really does take us six months I'm going to have a lot of explaining to do to my wife," said Andrew unhappily.
"Don't be such a grouch," said Cheval happily, giving him a clap on the back. "You'll be a hero. The man who helped enable The Return. The man who helped mankind achieve its manifest destiny to explore the galaxy. People will be talking about you for centuries to come."
"If the second Mars colony succeeds," replied Andrew gloomily. "If it doesn't suffer the same fate as the first. Do you ever wonder whether Fox is right to be doing what he's doing?"
"Not for a moment," the Sergeant replied, "and neither do you. Come on, let's bet back under way. We've got a fugitive to catch."
Andrew nodded and took the rover back to the tracks Fox's rover had left in the ice.