But the two advancing Styx stopped in their tracks and let out screams like fingernails being dragged down a blackboard. They staggered back blindly, trying to cover their eyes.

  This gave Will the opportunity he was looking for. He yanked Chester over, pulling him from the crank handle.

  But already the light was dwindling, and another two Styx were pushing aside their blinded comrades. They lunged at Will, their clawlike fingers raking out toward him. As he continued to pull on one of Chester's arms both Styx had latched on to the other. It turned into a tug-of-war between Will and the Styx, with the terrified whimpering Chester caught in the middle. Worse still, now that nobody was bracing the crank handle, it was whirring wildly around as the massive door sank slowly down on its runners. And Chester was right in its path.

  "Push them off!" Will cried.

  Chester tried to kick out, but it was no use; they had too strong a hold on him. Will wedged himself against the door in a vain attempt to slow its progress, but it was just too heavy and nearly unbalanced him. There was no way he could do anything about it and save Chester at the same time.

  As the Styx grunted and strained, and Chester tried with all his might to resist, Will knew the Styx couldn't be beaten. Chester was slipping out of his hands and screaming in pain as the Styx's fingernails bit deep into the flesh of his arm.

  Then, as the door continued its relentless descent, the realization hit Will — Chester was going to be crushed unless he let go.

  Unless he released Chester to the Styx. The crank handle was spinning madly. The door was little more than three feet from the ground, and Chester was doubled over — its entire weight pressing down on his back. Will had to do something and quick.

  "Chester, I'm sorry!" Will screamed.

  For an instant, Chester stared with horror-stricken eyes into those of his friend, and then Will let go of his arm and he flew straight back into the Styx, the momentum bowling them over in a tumbling confusion of arms and legs. Chester shouted Will's name once as the door clanged down with a terrible finality. Will could only watch numbly through the milky glass of the porthole as Chester and the Styx came to rest in a heap against the wall. One of the Styx immediately picked himself up and raced back toward the door.

  "JAM THE HANDLE!" Cal's shout galvanized Will. As Cal held a light orb, Will set to work on the mechanism by the side of the door. He whipped out his penknife and, using the largest blade, attempted to wedge the gear wheels with it.

  "Please, please work!" Will begged. He tried several places before the blade slipped in between two of the largest gear wheels and stayed in place. Will took his hands away, praying it would do the trick. And it did, the little red penknife quivering as the Styx applied pressure to the handle on the other side.

  Will glanced through the porthole again. Like some macabre silent film, he couldn't help but watch the desperation on Chester's face as he valiantly battled with the Styx. He'd somehow managed to get hold of Will's shovel and was trying to beat them off with it. But he was overpowered by their sheer numbers as they swarmed over him with the intent of devouring locusts.

  But then one face blocked out everything else as it loomed in the porthole.

  Rebecca's face. She pursed her lips sternly and shook her head at Will, as if she was telling him off. Just like she'd done for all those years in Highfield. She was saying something, but it was inaudible through the door.

  "We have to go, Will. They'll get it open," Cal said urgently. Will tore his eyes away with difficulty. She was still mouthing something at him. And with a sudden, chilling realization, he knew just what it was. Exactly what it was. She was singing to him.

  "'Sunshine'…!" he said bitterly. "'You are my sunshine!'"

  They fled down the rock passage with Bartleby bringing up the rear, and eventually came to a dome-shaped atrium with numerous passages leading off it. Everything was rounded and smoothed, as if eons of flowing water had rubbed away any sharp edges. It was dry now, every surface coated in an abrasive silt, like powdered glass.

  "We've only got one mask," Will said suddenly to Cal, as the realization hit him. He took the canvas and rubber contraption from his brother and examined it.

  "Oh, no!" Cal's face dropped. "What do we do now? We can't go back."

  "The air in the Eternal City," Will said, "what's wrong with it?"

  "Uncle Tam says there was some sort of plague. It killed off all the people…"

  "But it's not still there, is it?" Will asked quickly, dreading the answer.

  Cal nodded slowly. "Tam says it is."

  "Then you're using the mask."

  "No way!"

  In a flash, Will whipped the mask over Cal's head, muffling his protests. Cal struggled, trying to take it off, but Will wouldn't let him.

  "I mean it! You're going to wear it," Will insisted. "I'm the oldest, so I get to choose."

  At this Cal stopped resisting, his eyes peeking anxiously through the glass strip as Will made sure the hood was seated correctly on his shoulders. Then he buckled up the leather strap to secure the pipes and stubby filter around his brother's chest. He tried not to think what the implications of letting Cal have the mask might be for himself, and could only hope that the plague was yet another of the Colonist's superstitions, of which there seemed to be so many.

  Then Will slipped out the map Tam had given him from inside his boot, counted the tunnels in front of them, and pointed to the one they were to take.

  "How did the Styx girl know you?" Cal's voice was indistinct through the hood.

  "My sister," Will lowered the map and looked at him. "That was my sister" — he spat contemptuously — "or so I used to think."

  Cal didn't show any sign of surprise, but Will could see just how frightened he was by the way he kept glancing at the stretch of tunnel behind them. "The door won't hold them for long," his brother added, looking nervously at Will.

  "Chester…," Will began hopelessly, then fell silent.

  "There was nothing we could've done to help him. We were lucky to get out of there alive."

  "Maybe," Will said as he rechecked the map. He knew he didn't have time to think about Chester, not right now, but after all the risks he'd taken to save his friend the whole exercise had failed horribly, and he was finding it hard to focus on what to do next. He took a deep breath. "I guess we should go, then."

  And so the two boys, with the cat trailing behind, broke into a steady trot, penetrating deeper into the complex of underground tunnels that would eventually lead them to the Eternal City — and then, Will hoped, out into the sunlight again.

  Part Three

  The Eternal City

  30

  One two, one two, one, one, one two.

  As they jogged along, Will had settled into the easy rhythm he frequently used for the more strenuous bouts of digging back in Highfield. The tunnels were dry and silent; there wasn't the slightest sign that anything lived down here. And as their feet tramped over the sandy floors, not once did Will catch sight of any airborne dust or motes behind them in the beam of his light orb. It was as if their passage had gone completely unnoticed.

  But it wasn't long before he began to spot the faintest scintillations before his eyes, smears of light that materialized and then, just as abruptly, vanished from his field of vision. He watched, fascinated, until it dawned on him that something was not quite right. At the same time a dull ache gripped his chest, and a clammy sweat broke out on his temples.

  One two, one two, one… one… one two…

  He slowed his pace, feeling the resistance as he drew breath. It was peculiar; he couldn't quite put his finger on what was wrong. At first he thought it was simply exhaustion, but no, it was more than that. It was as if the air, having lain undisturbed in these deep tunnels, maybe ever since prehistoric times, was behaving like a sluggish fluid.

  One two, one…

  Will came to an abrupt halt, loosening his collar and massaging his shoulders under the straps of his
backpack. He had an almost irresistible urge to throw the weight off his back — it made him feel constricted and uneasy. And the walls of the passage bothered him — they were too close, they were smothering him. He backed away into the middle of the tunnel, where he leaned on his knees and took in several gulps of air. After a while, he felt a little better and forced himself to straighten up.

  "What's wrong?" Cal asked, eyeing him worriedly through the glass slit of his mask.

  "Nothing," Will replied as he fumbled in his pocket for the map. He didn't want to admit to any weakness, certainly not to his brother. "I… I just need to check our position."

  He'd taken it upon himself to navigate their route through the many twists and turns, aware that a single mistake would lose them in this subterranean maze of such extraordinary complexity. He remembered how Tam had referred to it as the "Labyrinth" and likened it to pumice stone with innumerable interlocking pores worming randomly through it. At the time, Will hadn't thought much about his uncle's words, but he now knew precisely what he'd meant. The sheer scale of the area was daunting, and although they had been making good time as they were moving rapidly through the passages, Will figured they had a long way yet to go. They were helped considerably by a gentle downward gradient, but this in itself caused him some consternation; he was only too aware that every foot they descended now would have to be climbed again before they reached the surface.

  He glanced from the map to the walls. They had a pinkish hue to them, probably due to the presence of iron deposits, which could explain why his compass was worse than useless down here. The needle dithered lazily around the dial, never settling in the same position long enough to give any sort of reading.

  As Will looked around him, he reflected that the passages could have been formed by gas trapped under a solidified plug of some kind, as it tried to escape through the still-molten volcanic rock. Yes, that could be the reason there weren't any vertical tunnels. Or possibly they'd been formed by water exploiting lines of weakness in the millennia after the rock cooled. I wonder what Dad would make of this, he thought before he could stop himself, his face falling as he realized that he'd probably never see his father again. Not now.

  And try as he might, he couldn't stop remembering that last glimpse of Chester as he'd rolled helplessly across the floor, straight back into the clutches of the Styx. Will had let him down yet again…

  And Rebecca! There it was, incontrovertible, he'd seen it with his own eyes. She was a Styx. Despite the fact that he felt so weak, Will's blood boiled. He wanted to laugh out loud as he thought back to how worried he'd been about her.

  But there was no time to reflect now — if he and Cal were going to get through this alive, he had to make sure they didn't stray off course. He took one last glance at the map and refolded it before they resumed their journey.

  One two, one two, one, one, one two.

  As their feet cruched in the fine red sand, Will longed for a change, a landmark, anything to break the monotony, to confirm that they were still on the right track. He began to despair that they were ever going to reach the end. For all he knew, they could be going around in circles.

  He was thrilled when they eventually came across what looked like a small headstone, with a flat face and a rounded top, set against the passage wall. With Cal looking on, he crouched down to brush the sand from its surface.

  A sweep of his hand revealed a symbol carved into the pink rock about halfway down the face. It was comprised of three diverging lines, which fanned out like rising rays or the prongs of a trident. Below were two rows of angular lettering. The symbols were unfamiliar and made no sense to him at all.

  "What's this? Some kind of marker or milestone?" Will looked up at his brother, who shrugged his shoulders unhelpfully.

  * * * * *

  Several hours later, the going had become slow and laborious. They came to fork after fork in the tunnel, and Will had to consult the map even more frequently. They'd already taken one wrong turn; luckily they hadn't gone too far before Will realized his mistake and they had painstakingly retraced their steps and found their way back to the correct path again. Once there, they had flopped onto the sandy floor, stopping just long enough to catch their breath. Although he was trying to fight it, Will felt unusually tired, as if he were running on empty. And when they resumed their journey, he felt weaker than ever.

  Whatever state he was in, though, Will didn't want Cal to suspect anything was wrong. He knew they must keep going; they must keep ahead of the Styx; they had to get out. He turned to his brother beside him.

  "So what does Tam do in this Eternal City?" he said, breathing heavily. "He was very cagey when I asked him about it."

  "He searches for coins and stuff like that, gold and silver," Cal said, then added, "most of it from graves."

  "Graves?"

  Cal nodded. "In the burial grounds."

  "So people really lived there?"

  "A long time ago. He thinks that several races occupied it, one after the other, each building on top of the last. He says there are fortunes just waiting to be found."

  "But who were these people?"

  "Tam told me the Bruteans were the first, centuries ago. I think he said they were Trojans. They constructed it as a stronghold or something, while the Topsoil London was built above.:

  "So the two cities were connected?"

  Cal's mask nodded ponderously. "In the beginning. Later the entrances were blocked up, and the stones marking them were lost… The Eternal City was just forgotten," he said, puffing noisily through the air filter. He looked nervously back up the tunnel, as if he'd heard something.

  Will immediately followed his glance, but all he could see was the shadowy form of Bartleby as he loped impatiently from one side of the tunnel to the other. It was clear that he wanted to go faster than the two boys, and from time to time he would speed past them but then stop to sniff at a crevice or the ground up ahead, often becoming visibly agitated and letting out a low whine.

  "At least the Styx will never find us in this place," Will said confidently.

  "Don't count on it. They'll be following us, all right," Cal said. "And then there's still the Division in front of us."

  "The what? "

  "The Styx Division. They're sort of a… well… border guard," Cal said, searching for the right words. "They patrol the old city."

  "What for? I thought it was empty."

  "There's talk that they're rebuilding whole areas and patching up the cavern walls. It's said that the whole Colony might be moved there, and there's rumors of work parties of condemned prisoners, toiling like slaves. It's only rumors, though — no one knows for sure."

  "Tam never mentioned anything about more Styx," Will didn't attempt to hide the alarm in his voice. "Bloody brilliant," he said angrily, kicking a rock in his path.

  "Well, maybe he didn't think it would be a problem. We didn't exactly leave the Colony quietly, did we? Don't get too worried, though; it's a huge area to cover and there'll only be a handful of patrols."

  "Oh, great! That's a real comfort!" Will replied as he imagined what might be in store for them ahead.

  They wandered on for several hours, eventually scrabbling down a steep incline, their feet slipping and sliding in the red sand until they finally reached a level area. Will knew that if he'd been reading the map correctly they should be approaching the end of the Labyrinth. But the tunnel narrowed before them and appeared to end in a blind alley.

  Fearing the worst, Will raced ahead, stooping as the roof lowered. To his relief, he found that there was a small passage to one side. He waited until Cal caught up, and they looked apprehensively at each other as Bartleby sniffed the air. Will hesitated, looking repeatedly from Tam's map to the opening and back again. Then he met Cal's eyes and smiled broadly as he edged into the narrow passageway. It was bathed in a subdued green light.

  "Careful," Cal warned.

  But Will was already at the corner. He became aware of
a familiar sound: the patter of falling water. He moved his head until just one eye was peering around the edge. He was struck dumb by what he glimpsed, and inched slowly into the open, into the bottle-green glow, to get a better view. From Tam's description, and the pictures his imagination had conjured up, he was expecting something out of the ordinary. But nothing could have prepared him for the sight that met his eyes.

  "The Eternal City," he whispered to himself as he began to move down a huge escarpment. As he looked up, his wide eyes scrutinizing the roof of the immense domed space, water splashed onto his upturned face and made him flinch.

  "Underground rain?" he muttered, immediately realizing how ridiculous that sounded. He blinked as it dripped into his eyes, stinging them.

  "It's seepage from above," Cal said, coming to a halt behind him.

  But Will wasn't listening. He was finding it hard to come to terms with the titanic volume of the cavern, so massive that its farthest reaches were hidden by fog and the mists of distance. The drizzle continued to fall in slow, languorous swathes as they set off again down the escarpment.

  It was almost too much to take in. Basaltic columns, like windowless skyscrapers, arced down from the mammoth span of the roof into the center of the city. Others speared upward from the outlying ground in mind-bending curves, encasing the city with gigantic undulating buttresses. It dwarfed any of the Colony's caverns with its scale, and brought to Will's mind the image of a gargantuan heart, its chambers crisscrossed by huge heartstringlike columns.

  He pocketed the light orb and instinctively sought the source of the emerald green glow that gave the scene a dreamlike quality. It was as though he were looking at a lost city in the depths of an ocean. He couldn't be sure, but the light seemed to be coming from the very walls themselves — so subtly that at first he thought they were simply reflecting it.