After a few hours they stopped for a bite to eat and a drink. The trail rations were rather dry and they needed to take a sip or two of water to moisten their mouths first, all the while trying to stop quivering droplets of water from floating out of their bottles like soap bubbles. None of them were feeling very thirsty, though, so they decided to ration their water, having no idea how long it would be before they were able to refill their bottles. In such low gravity, the water in the tunnel no longer pooled on the floor but formed a thin film of dampness all over the mossy walls, spread far too thin for them to be able to collect it.

     Sanitation also presented a problem, as they discovered when they tried to relieve themselves, an experience that turned out to be unpleasantly like standing too close to a waterfall except that the droplets were bigger. After some thought and head scratching, they carefully transferred water from one bottle to another until they had an empty one, which the men then took turns to fill, taking it some distance back down the tunnel to empty it on the moss, shaking it out as carefully as possible so that as little as possible of the contents were left floating about in the air. It was more difficult for the women, but they took the bottle out of sight to the other side of an airlock and came back a couple of minutes later saying they’d solved the problem. Thomas was curious to know how they’d done it, but thought it better not to ask.

     They set off again shortly afterwards, all of them keen to get to wherever they were going as soon as possible. They came to several more closed and locked airlocks, blocked by vacuum, and were forced to take a rather circuitous route to get past them.

     "I'm not sure we're still going in the right direction," said Jerry, frowning with concern. "I'm worried we might have gotten turned around."

     "You mean we might be going back to the city?" said Matthew, his eyes widening with fear.

     "I'm just saying it's hard to keep my sense of direction straight," the nome replied, looking both ways up and down the tunnel. I think we’re still heading away from the city, but I think we ought to be prepared for the possibility that... You know."

     "Just do the best you can," said Thomas. "Nobody's expecting miracles from you."

     Suddenly Lirenna came to a dead stop, and the tiny nome bumped his head on the shae’s feet. “What is it?” he asked.

     “I can smell something!” she said, angling her head and taking long sniffs. “I think it’s a forest. Some kind of greenery anyway. I can smell damp and wet leaves and moss. A forest!”

     A dawning delight was spreading across her face, but the others shared concerned looks. They’d thought she was getting better. Could this be a symptom that her condition was getting worse? Had she actually begun hallucinating now?

     “Actually, I think I might be smelling something as well,” said Diana, though. “Can’t really place it… It might be damp forest, or something that smells like it.”

     “We’re on the smallest moon,” said Thomas carefully. “In an underground tunnel…”

     “Yes, yes!” snapped the cleric angrily. “I know it can’t actually be a forest, but there’s something…”

     “It’s just the power of suggestion,” said the wizard doubtfully. “One person says they smell something and everyone else can suddenly smell it as well, but it’s just in your head.”

     “I’m not imagining it!” insisted Lirenna though. “Let’s go, see what it is.”

     She hurried ahead and the others hurried to keep up with her. A moment later, though, they stopped again, all frozen in fear. There was a light up ahead. Something, hidden by a curve in the tunnel, was illuminating the tunnel wall.

     “What is it?” asked Matthew fearfully. “Konnens?”

     They tensed up in fear, expecting to see a Konnen patrol come into view, lighting their way with their portable glowing globes of marble. The light source didn’t move, though, and after a few minutes they relaxed as no immediate danger presented itself.

     “Maybe they’ve made camp,” whispered Jerry. “Having lunch or something.”

     “No, I don’t think so,” replied Thomas, however. “That doesn’t look like marble light. It looks more like, like...” His voice trailed off. The possibility that had entered his head was too crazy to be true.

     Lirenna completed the thought, however. “Like natural sunlight!” she cried excitedly. “It looks like natural sunlight!”

     “It can’t be,” replied Thomas however. “We’re over a hundred yards below the surface, probably more like two hundred yards.”

     “I don’t care!” insisted the demi shae. “I know natural sunlight when I see it! And the smell’s stronger. Come on, let’s go see!”

     She propelled herself forward, kicking herself off the rungs, and shot out of reach before Thomas could grab her ankle and stop her.

     “Lenny!” he called out. “Don’t be crazy! It could be anything up there!”

     Shaun grabbed hold of her arm as she sped past and pulled her in, holding onto a rung with his other hand. “He’s right,” he agreed as he fought to hold onto the struggling demi shae. “We’ve got to move carefully. You can go first if you want, but we must go slowly in case it turns out to be something nasty. Okay?”

     Gradually his words sank in and she relaxed, nodding slowly. “Alright,” she said. “but let’s go now! There’s no point waiting, is there?”

     She took hold of the rungs again and moved off along them, the others following behind. A couple of times she pulled out ahead and Shaun had to grab her ankle to slow her down, but on the whole she kept to a sensible speed, being intelligent enough to know the dangers of hurrying into the unknown.

     As they got closer, they came across patches of ordinary green moss among the dark coloured mana moss, as well as ferns, liverworts and other conventional photosynthesising plants, confirming their suspicion that the light was a permanent feature of this part of the tunnel. There was a corresponding increase in the amount of animal life. Rats and other small rodents scurried away as they approached, grasping hold of fronds and stalks with their amazingly dextrous claws, and the air was filled with clouds of flying beetles and other insects, the versatile little creatures having apparently mastered the trick of flying in low gravity.

     Then they turned a bend in the tunnel and finally saw the source of the light. Starting about fifty yards away, and running as far as they could see, there were hemispheres of frosted glass set in the ceiling, each one shining with natural sunlight.

     “Glowbottles!” said Matthew excitedly.

     “No, I don’t think so,” said Thomas, however.

     They reached the nearest and gathered around it, holding onto the rungs in the ceiling and each other to resist the feeble gravity that tried to pull them back down to the ground. The glass hemisphere was about twelve inches across and seemed to be merely a covering to protect the true source of the light inside.

     Thomas felt around its edge, pulling away the moss that had tried to cover it, and found that it was attached to the ceiling by four screws. None of them had ever seen screws before, but the intelligent wizard soon figured out what they were and began to unscrew them with his table knife, taking care to avoid the sharp edge he’d made by rubbing it against a patch of bare rock. He got one screw out and handed it to Shaun, who examined it in fascination.

     “What a good idea!” he exclaimed. “I wonder why no-one else ever thought of it.”

     Thomas soon got the other screws out and gently prised the glass bowl out of its setting against the tangles of moss that tried to hold it in place. As it came free the truth was revealed and they saw a cluster of optical fibres protruding from a hole in the ceiling, each of the thousands of fibres having a tiny point of sunlight on its tip.

     “So that’s how it’s done,” said Thomas excitedly. “These fibres must go all the way up to the surface. See how the hole’s been plugged with some kind of resin to stop the air escaping.”

     “There must be a set of mirrors up on the surface to reflect the sunlight onto the other ends of these fibres,” agreed Jerry. “Think of the expense though. If each of these fibres is a hundred yards long, then there must be at least a hundred miles of fibre here! And that’s just for this one light!” He gestured at the others spaced along the tunnel’s ceiling. “The Gods alone know how many there are.”

     “Yes, but the trogs only charge a high price because they’ve got a monopoly on the stuff," pointed out Thomas. "It doesn’t necessarily mean that it’s hard or expensive to make. In fact I think this proves that they can produce as much of it as they like. Angus hinted once that their cities are somehow lit by sunlight from the surface, and I bet this is how they do it. I bet all trog cities have cables of optical fibres like this.”

     “Wouldn’t it be simpler to just have a long straight hole with a mirror at the top to reflect the light down?” asked Matthew.

     “Bit dangerous, I’d have thought,” replied Thomas. “If the glass windows at each end broke, all the air would get out.” He put the glass bowl back in place and began to replace the screws.

     As he was doing this, Matthew borrowed a screw from Shaun and looked at it curiously. “Shaun,” he asked, “what kind of metal would you say this was?”

     “Iron, isn’t it?” replied his older brother. “No, on second thought it’s probably steel, since you might want to put a bit of force on it. Iron would probably shear off.”

     “Are you sure?” asked Matthew, however. “Have a closer look.”

     Shaun took a close look at one of the screws he still held, as Thomas took one to screw back in. It wasn’t steel, he realised. It wasn’t shiny enough. It had the dull grey appearance of pig iron, except that it didn’t exactly look like iron either. It was slightly the wrong shade of grey, and where the head of the screw had been exposed to the open air and started to corrode, the oxide wasn’t the characteristic reddish brown of rust. Instead, the head was covered by the thinnest possible layer of fine white powder.

     “You’re right,” he agreed. “It’s no metal I’ve ever seen before. Do you know what it is, Jerry?” He handed the screw across.

     “Never seen anything like it before in my life,” replied the tiny nome, equally baffled. “Must be some kind of strange moon metal. Pity Angus and Douglas aren’t here, they might have known what it was.”

     Thomas then took the screw from him to put it back in its proper place.

     Once he was finished replacing the bowl they prepared to move on, but Lirenna seemed reluctant to leave. She was staring at the light with an intensity Thomas didn’t like, and with her face so brightly illuminated he saw for the first time how pale she was. A pale skin might have been the height of fashion among the upper classes of human society, where only the lower classes worked outdoors and got suntanned, but on a sunloving shae woman it looked completely wrong and the sight of it tore Thomas’s heart.

     He drifted over to her and put a gentle hand on her shoulder. “Come on, Lenny. We’re not leaving the sunlight behind. Look, there’s plenty more lights up ahead. Come on now."

     The demi shae nodded, but it still took more urging before she was finally able to leave the light behind and allow Thomas to lead her gently along the tunnel.