Tired though they were, sleep was harder to come by than they’d thought because every slightest movement sent them bobbing up into the air like balloons, coming back down on one or another of their companions more often than not. In the absence of any reliable time reference, though, they simply remained in the airlock until they were all rested and refreshed, even though ten or twelve hours might have passed down on Tharia.

     Thomas was on watch with Diana when the lights in the ceiling faded to darkness, and it worried him for a while until he decided that it was simply due to Kronos’s orbit around Tharia. The optical fibre cables could only transmit sunlight down to the tunnels if there was sunlight on the surface, and since Kronos took eight hours to complete one orbit, this meant that there would be four hours of light followed by four hours of darkness and, sure enough, when he was woken up for his second watch, it was light again.

     They eventually decided by mutual consent that morning had come and prepared to face the new day. They had a small breakfast of trail rations, washed down with a swallow or two of water, after which the wizards read their spells, re-memorising those that had changed overnight. While they were doing that, Diana spent time in meditation and Shaun got Matthew to help him string the bow. He would leave it strung all the time, he decided. It would stretch the string, which would eventually leave it useless, but it was better than not being able to use it when they needed it. He wasn’t going to be caught out that way again.

     Thomas found that his web spell had changed, but he found it a real struggle to memorize the new words because he had a pounding headache that interfered with his concentration. It was a really bad one, as though there were someone trapped inside his skull trying to smash his way out with a sledgehammer, and as he rubbed his temples with his left hand he noticed Jerry doing the same thing. “Headache?” he asked with a wry grin.

     “Yeah,” replied the tiny nome. “You too?”

     “It’s all this concentrating on magic spells,” said Thomas. “Puts a strain on the eyes. How are you, Lenny?”

     “Fine, at the moment,” replied the demi shae. “A little tired, that’s all. Funny, just a moment ago I was fine, bursting with energy and eager to be off, but then I open my spellbook and all of a sudden...”

     “All of a sudden you find yourself wishing you could lie down again for a few minutes,” interrupted Shaun, and Lirenna’s eyes widened in surprise. “You feel that if you just close your eyes for a while you’ll be fine. Is that right?” She nodded.

     “Now that you mention it,” added Thomas, “I’m a little tired too. It’ll probably pass once we get moving.”

     They allowed themselves one more swallow of water each before they moved off. They still hadn’t found anywhere they could refill their water bottles, so they were trying to ration their water, make it last as long as possible. Fortunately none of them seemed to be getting at all thirsty, despite the dryness of their hard, biscuit-like trail rations, but as Thomas was relieving himself into an empty bottle on the other side of one of the doors it occurred to him that there was a lot more water leaving his body then there was entering it, especially if you took breath and perspiration into account.

     He looked at the contents of the bottle and was shocked by the deep, rich colour of it, something that normally meant that his kidneys were trying to conserve his body's water. He still wasn’t thirsty, though, so there couldn’t be much wrong with him and he put the matter out of his mind.

     Finally, they were all ready and they moved off, half floating, half pulling themselves along the sunlit, overgrown corridor. They remained alert and on the lookout for moontigers as they went, determined not to be caught by surprise again, as well as keeping a wary eye out for whatever other dangers might be lying in wait ahead of them. An hour after leaving the airlock the lights faded again as night fell on the surface above them and Thomas took his glowbottle out to light their way.

     They passed several more caverns and side tunnels as they went, some of which sloped upwards or downwards at fairly steep angles, and a couple of times they came across more of the circular shafts leading, so they assumed, all the way down to the very centre of Kronos where the moon trogs were said to live. One of the vertical tunnels had smooth, slippery sides like the one they'd used to escape from the dungeon and Thomas pointed it out to the others.

     "I wouldn't be surprised if we came across the creature responsible for this before long," he said as they left it behind. "We should be ready for it, just in case."

     "You said it was like the creature that made the wyrmhole," said Matthew, bringing himself to a halt to allow the wizard to pull level with him. "The hole we used to get down to the Underworld."

     "That would be my guess," the wizard replied. "Smaller, though. Like a mouse compared to a horse."

     "Why would the Agglemonians bring something like that up here?" asked Diana as the others gathered around them. They settled with their backs to the walls as they rested their arms, tired from pulling themselves along the tunnel.

     "Most likely it made its own way here," Thomas replied. "I would lay money that it comes originally from another universe. Magic is funny and unpredictable. The magical field that surrounds all the planets and moons and which penetrates several miles below their surfaces has eddies and whorls in it, like water flowing over a tumble of polished boulders in a mountain stream, and occasionally one such eddie spontaneously forms a semi-stable portal connecting our universe with a distant, alien dimension."

     Talking was making his mouth dry. He took his water bottle from his pocket, intending to take a sip, but it was only half full and he still wasn't really thirsty. He tucked it away regretfully.

     "Some of these dimensions have life of their own," he continued. The others weren't really paying attention, he knew, but that didn't matter. He just liked to talk. "It's often a radically different kind of life. Nothing like anything we're familiar with. Occasionally one of these creatures comes through, driven by curiosity, hunger, some danger behind them or some alien motive totally incomprehensible us. Most of them die as soon as they get here. The environment is just too different. Like a frog suddenly dumped in the desert, for instance, but every so often some survive and breed, forming a viable population that might survive for centuries, even millennia, before some aspect of the, to them, harsh, alien environment drives them to extinction."

     Lirenna was paying attention, he suddenly realised. She was studying his face with her huge, bright eyes and nodding along to every point he made. Thomas felt his heart beat faster and he smiled as he continued to talk.

     "It's possible that the creature that made these tunnels is that rarest of all extra-dimensional visitors. A creatures that found its new environment so similar to its natural home that it's thriving and multiplying like rabbits. The portal through which it came has almost certainly long since dissolved back into randomised magic, of course, leaving them stranded here, but it might not want to go back even if it could. If it came from one of the Planes of Stone then life here could be pretty near idyllic. No need to fear predators or competition from other, closely related species, all of which they've left behind in their natural home. The only things they have to fear is us. If they make a habit of making holes and letting the air out then they're probably hunted by the moon trogs, as well as the humans living in these tunnels. If we should come across one, it might well see us as a threat, therefore, and it might attack us."

     "Well, that's very interesting," said Shaun, gathering himself to move on. "But we're not getting any closer to safety by sitting here. We need to move on."

     Thomas nodded, and they continued their way along the tunnel.

☆☆☆

     They came acrossl more vertical tunnels later that day. Man made ones, to judge from their irregular, chipped surfaces. They debated whether or not to go down them, but decided again not to just yet as the vegetation covered all the handholds and if they fell it would be as fatal in Kronos’s low gravity as back on Tharia. Instead, therefore, they took the downward sloping tunnels whenever they came to them, preferring to go down by the slow but safe route.

     Slow it certainly was. Jerry’s sense of direction told him that, as the tunnels branched and turned, they were not moving a very great horizontal distance from the airlock where they’d spent the night, often passing below a tunnel they’d been in just a couple of hours before. What was more, as they got deeper below the surface of the tiny moon, they came upon more and more stretches of tunnel that were still in darkness, not having any lights in their ceilings. Evidently, the moon trogs were having some difficulties threading cables of optical fibre through so much moonrock.

     Lirenna grew increasingly sad and disappointed as the sunlit stretches of tunnel grew fewer and farther between, but Thomas was relieved when she didn’t lapse back into the terrible state of hopelessness and misery she’d suffered from in Kronosia. It seemed to be enough for her to know that there was sunlight and life somewhere in Kronos, and that they could go back to it anytime they wanted. Even the presence of the moontigers helped, Thomas mused, since they proved the existence of a thriving food chain, and predation was part of the natural world that she needed to have around her.

     They were in another sunlit stretches of tunnel, though, when Lirenna paused, her head cocked as if listening. "You okay?" asked Thomas, pushing himself to drift next to her.

     Before the demi shae could answer a crowd of rats dashed past them, some of them actually flying through the air with the aid of a membrane of skin stretched between their front and back legs, functioning perfectly adequately as wings in the low gravity. The Tharians thought they were being attacked and readied their spells and weapons, but the rats simply passed them by, hurrying away down the tunnel as if all the fiends of hell were after them.

     “What in the world...” began Matthew, but Lirenna hushed him to silence and listened intently. They all listened, but none of the others could hear a thing and after a few moments Thomas pulled himself alongside her. “What is it?” he asked.

     “There’s something up ahead,” replied the demi shae. “I don’t know what, but it’s making some kind of slithering sound, like something being dragged along bare rock.”

     Thomas listened again, but he could still hear nothing. “How far away is it?” he asked.

     “Can’t tell exactly,” replied Lirenna, “but not far. About fifteen, twenty yards.”

     “Impossible!” said Shaun. The tunnel ran straight as a ruler both ahead and behind them, and they could see as far as the nearest airlocks in both directions. The one in front of them was a hundred yards away while the one behind was three times that distance, and as far as they could tell there was nothing in between except themselves. “Look, there’s nothing there.”

     “I can hear it,” insisted the demi shae. “It’s getting louder. You must be able to hear it now.”

     “Yes, I can hear something,” agreed Jerry. “A slithering, scraping sound, like a giant snake crawling along bare rock. It’s coming from up ahead, I think.”

     “Is it getting nearer?” asked Shaun, drawing his sword.

     “No,” replied Lirenna. “Just louder.”

     “Louder but no nearer?” said Shaun. “What in the world could it be?”

     “Dunno, but the rats didn’t like it,” replied Thomas. “I think we should get out of here while we still can.”

     “What’s happened to your famous curiosity?” asked Jerry, grinning.

     “It’s out to lunch,” said Thomas. “Come on, let’s go.” They turned around and headed back the way they’d come.

     They hadn’t gone more than a few yards, though, when there came a louder noise, one that they all heard. It was a hissing noise, like the hissing of a snake, but it went on and on, getting steadily louder. It was horribly familiar to the Tharians, but for a moment they couldn’t put their fingers on it and they could only freeze in horror, certain that something dreadful was about to happen.

     "It's like the sound it makes when there's air passing through an airlock door," said Matthew, sounding disturbed. "Could it be air getting out somewhere?"

     They all glanced fearfully at each other as they remembered the scene of death and mutilation they'd seen in the park cavern. The shriveled, shrunken corpses, their jaws gaping open in endless, silent screams. They remembered the piles of corpses piled up against airlock doors. Men, women and, worst of all, children, lying where they'd crowded and trampled each other in their desperation to escape. They remembered looking up and seeing the huge fissure in the ceiling through which the stars had been shining, a sight that had struck them, even then, as being terribly wrong, even though at the time they’d known nothing at all about air and vacuum.

     Thomas's hand went to his throat, as if praying to all the Gods that a Necklace of Vacuum Breathing might somehow have miraculously appeared there. “By the Gods, no!” he whispered, pale and sweating with fear. “Air leak!”

     “What?” asked Shaun, looking around. “What is it? You look terrible!”

     “Air leak!” screamed Thomas. “There’s an air leak! We’ve gotta get outta here!” He stared at Lirenna, who was staring back at him with wide, frightened eyes. "Move!" he told her. "Quick!"

     “He could be right,” agreed Jerry as the hissing grew louder. There was now a slight movement of air in the tunnel and small pieces of detritus, dead leaves and the like, were gently lifted from the ground and carried to a spot on the ceiling. “We’ve got to get to an airlock quick. Not that way, Matt! The one up ahead’s much closer!”

     The soldier, who'd begun pulling himself back the way they'd come, heard him and grabbed a branch of shrubbery to bring himself to a halt. Then he began pushing himself back in the other direction.

     They hurried along the tunnel as fast as they could, pulling themselves along with a desperation that grew with the hissing of escaping air. As they passed the spot on the ceiling where the cloud of detritus was gathering, Thomas kicked himself up towards it, thinking he could perhaps block it with something, but as he passed within a few feet of it he saw something that turned his heart to ice and froze him in terror.

     Part of the ceiling was bulging inwards, like rubber being pressed in by some force from outside, and it was beginning to crack and split open. The cracks widened as the force increased, letting the air out even faster, and as he moved closer for a better look he saw movement in one of the cracks. There was something alive in there. Some kind of animal. Something that didn’t need air to breathe and that was trying to break its way into the tunnel. He floated there, carried slowly closer by the movement of air, hypnotised in helpless terror as a long, thin tentacle slid through one of the cracks and felt its way around in the vegetation.

     Then a hand grabbed his ankle, startling him witless. “Tom! Come on!” shouted Shaun, and he came to his senses with a snap, scrambling away after the others.

     They looked around from time to time as they fled and saw more tentacles pushing their way through the widening hole. The rock seemed to have turned as soft as warm toffee and the creature, whatever it was, was able to push it aside to make room for its main body, which now began to come through head first. The widest part of its body was still blocking the hole, plugging it and slowing down the escape of air, but soon it would be through, leaving a three foot wide hole behind it which must connect with the surface somehow, and then it would only be a matter of seconds before the tunnel was in vacuum and every living thing in it was dead.

     The last bit of resistance in the ceiling gave way and the creature’s head oozed in, distorting as it squeezed through the narrow gap and expanding back to its normal shape once it was through. There was a rubbery, rubbing sound as the soft, boneless creature literally flowed into the tunnel, but it was forced to pause as the widest part of its body became caught in the narrow opening and it had to wait and use its ability to soften rock again before it could continue. Thomas looked back and saw what looked like a six foot caterpillar with tentacles dangling from the ceiling, pulling itself through inch by inch, and he looked ahead to see the airlock still an impossible distance ahead of them. He gave a little shriek of fear and hurried forward with even greater speed…