The sun rose again and set again before they awoke. When Thomas finally opened his eyes he found Lirenna still asleep beside him, and as so many times before he was literally struck dumb by her grace and beauty, far surpassing that of any merely human woman. Her slow deterioration, the gradual loss of her vitality and joy of living that had accompanied her distress at being confined underground for so long had been so slow and insidious that he’d barely noticed it, but it had only taken one night under the stars for her to recover completely and she was now so radiant, so alive, that Thomas thought he was still dreaming.

     The others saw him staring dreamily at her and grinned at each other in amusement, until Diana gave them a sharp poke and scowled at them in rebuke.

     They were having a breakfast of trail rations when Ban-Chin returned. “Is this what you’ve been eating?” he asked in surprise, taking one of Jerry’s biscuits and examining it closely.

     “Yes,” replied Shaun. “Why?”

     “No wonder you nearly died of dehydration!” said the moon trog, shaking his head in wonder. “This stuff’ll kill you!”

     “We were told it contained everything necessary to sustain life,” protested Jerry.

     “Maybe, everything except water,” replied Ban-Chin. “The human renegades survive by eating ordinary food; the animals and plants they find in the tunnels and caverns. They contain all the water you need to survive. To live on this stuff, you’d need to carry gallons of water around with you everywhere you go.”

     There was a sudden loud smack that made them all jump, and they looked around in surprise. “What was that?” asked Matthew.

     “Micrometeorite impact,” replied the moon trog casually. He indicated one of the dome’s triangular panes of crystal and they saw a pit in its outer surface that hadn’t been there before. A pit about an inch wide and half an inch deep. “Dust from the comets,” he explained. “You get used to it. Impacts big enough to break all three layers are rare.”

     The Tharians suddenly felt rather uncomfortable and anxious to get underground again, even Lirenna. “Er, what happens when a pane breaks?” asked Thomas nervously.

     “We just replace it,” replied Ban-Chin. “It would take about ten hazads, that’s about ten day, night cycles, for all the air in a dome to escape through a broken pane, so there’s no hurry. We usually get a new pane in place within two or three hours. Every so often, though, there’s a more serious impact, sometimes big enough to destroy an entire dome and kill everyone in it. The most serious incident so far happened about fifty years ago. A fragment of a comet came down about five miles from here and half our domes were destroyed all at once. We went through a time of great famine after that, and it was many years before things got back to normal.”

     “The great disaster,” exclaimed Diana. “The great disaster that hit the city.”

     “Yes,” agreed the moon trog. “We heard that you humans suffered as well. Let’s hope that it's a long time before something like that happens again. We’re determined not to be caught out like that again, though. We were lucky the last time. If every dome containing livestock had been destroyed, then all our farm animals would have become extinct, or we might have lost every dome containing grasses and have to spend the rest of eternity without wheat, maize or corn. As it was, though, we lost some of every kind of dome, and some of every kind survived. Ever since then, though, we keep seeds of every plant in storage caverns deep in the centre of Kronos, and keep some of every kind of livestock as pets in our homes, so that if another great disaster hits we’ll be sure not to lose any more species. Also, we have enough food in storage to last us until we can rebuild enough domes to grow more. If, the Gods forbid, it does ever happen again, we’re determined to be able to shrug our shoulders and just rebuild and carry on. We’re not going to suffer another famine like the last time.”

     “Hey, wait a minute!” protested Matthew. “How do you replace broken panes? And how do you build these domes in the first place? You’d need to be able to walk around on the surface, where there’s no air.”

     “They must have Necklaces of Vacuum Breathing,” said Thomas. “Like we used to get through the park caverns.”

     “No,” said the moon trog, though. “We used to have some. The Agglemonian wizards gave them to us and we used them to build the first domes, but they stopped working, one by one. Some say that they were defective in the first place. This was hundreds of years before the city was created. The ones possessed by the human noble families were created long after ours, and the wizards may have improved upon them. No, we wear suits that completely enclose our bodies and hold the air in, along with bottles containing air to breathe on our backs. We call them air suits, and wearing them we can move around on the surface for up to an hour at a time.”

     “Incredible!” said Thomas, considerably impressed. “You’ve achieved wonders up here! And to think that no-one back on Tharia even knows you exist!”

     “That’s right,” agreed the moon trog. “And that’s the way we’d like to keep it. Our greatest grief is that there are humans up here on Kronos with us. There was nothing we could do to prevent that, but it's still our dream that we might, one day, have Kronos all to ourselves."

     “The Kronosians want to go back to Tharia,” pointed out Diana. “If you helped them, and us, to go back, then you’d be rid of all of us. We’d all get what we want.”

     “Yes, but then there’d be people back on Tharia who knew about us,” pointed out Ban-Chin, “and your wizards have the ability to teleport over any distance, even across space from Tharia to Kronos. Even if we destroyed the teleportation cubicle, you would be back one day, to get more iron. No, we just have to endure your presence on our world, in order to keep the rest of humanity ignorant of us.”

     Their hearts fell. It was now clear that the moon trogs, friendly though they seemed, would actively block their attempts to go home. They’d just have to go on making their plans in secret. It was something they hated getting used to.

     More moon trogs appeared. A dozen of them, wearing padded body armour and with blowpipes and boxes of poison darts hanging from their belts. “You must come with us,” said their leader, distinguished by the monkey hair crest on the top of his leather helmet.

     “Well, looks like it’s goodbye,” said Ban-Chin regretfully. “It’s been fun talking to you. Maybe we’ll meet again some day.”

     “You never know,” replied Shaun. “We’ll never be more than twenty five miles away. Thanks again for saving us.”

     The others also added their thanks, which Ban Chin graciously acknowledged before making his apologies and leaving. The guardsmen then politely asked for their weapons, and they handed them across without comment, knowing there was nothing to gain by objecting. The moon trogs then led them back to the entrance of the tunnel, out of the farm dome and back down into the depths of Kronos. They tried to talk to the guardsmen, but the moon trogs replied only in monosyllables, if they answered at all, and the Tharians got the uncomfortable feeling that they were under arrest. Much of their enthusiasm and relief at having made contact with the moon trogs had now faded away, and they were beginning to wonder if coming here had been such a good idea after all.

     The tunnel curved very gently downwards as the miles passed, maintaining the same angle to the centre of Kronos as they descended. The bare moonrock from which it had been carved changed colour as well, darkening as the proportion of iron to rock increased, and here and there were silvery streaks of pure iron, becoming more frequent as they descended.

     The moon trogs would no doubt have gone the whole way in one leg but the Tharians, who were still getting used to this method of travel, were soon feeling tired and so their guards (or captors?) allowed them to stop and rest after a couple of hours. As they allowed themselves to settle onto the bare rock of the tunnel floor, Thomas found himself fascinated by a streak of iron under his feet. It seemed to have detail to it. Some kind of structure, as if it had once been some kind of intricate iron device before being heated and partially melted. “Look at this,” he said curiously.

     The others gathered around to look at it. “Looks like it used to be something,” Shaun agreed. “Like a box or something, before it was crushed and melted.”

     “It's partially merged with the rock around it,” Jerry observed. “The rock must have been molten as well. There's another one, here.” He indicated another suspiciously regular streak of iron in another part of the floor. “We must be a couple of miles down by now. How could the rock this deep have melted?”

     “Do your people know anything about this?” Thomas asked the guard.

     “We're just policemen,” the moon trog replied. “We just do our jobs and mind our own businesses.”

     “You must know if these… these iron… these relics are common. Can they be found anywhere else within Kronos?”

     “They’re everywhere,” the trog replied. “Mere curiosities, of no importance.”

     “On the contrary!” said the wizard, though. “Don't you see? It means that someone else lived here once. Before the moon trogs, before the Agglemonians. One of the pre-human civilisations, perhaps. Millions of years ago. They dug tunnels, built devices of iron, and then it was all destroyed. Melted. The amount of heat that must have been required…” He turned back to the moon trogs. “You say there's more iron in the rock the deeper you go?”

     The moon trog just nodded. “You know what?” said the wizard. “I think the whole moon was once completely melted. All of it, from the surface right to the core. Molten iron is heavier than molten rock and began to sink. It would all have sunk right to the centre but the moon cooled down and solidified before the process could be completed.”

     “Maybe,” agreed Shaun. “So what?”

     Thomas stared at him in disbelief. “So what? Don’t you see? The power those ancient people must have possessed… The achievements they must have attained…”

     “Maybe,” said the woodsman, “but so what? They're gone now. Nothing but relics left behind. Tunnels on Tharia, tunnels up here on Kronos… What matters is the here and now. The situation we’re in. How about we focus all our minds on that?”

     Thomas just stared at him, astonished that anyone could have so little imagination, but then the moon trogs told them that they'd rested long enough. It was time to move on. The Tharians roused themselves, therefore, and followed the moon trogs further down into the depths of the smallest moon.