Curiosity overcame him, and he leaned over to one of the boys walking beside him and asked in a low voice, "Excuse me, what's that thing you've got there?"

The boy glared charily at him and muttered, "It's a pitch cleaver, of course."

"A pitch cleaver," Will repeated. "Uh, thanks," he added as the boy deliberately slowed his pace, dropping back from him. At that point, Will felt more alone than he could ever remember and was suddenly overwhelmed by the strongest yearning to turn around and go back to the Jerome house. But he knew he had no alternative but to do what he was told down here in this place. He had to toe the line.

Eventually they entered a tunnel, the tramping of their boots echoing around them. The tunnel walls haad diagonal veins of a shiny black rock running through them, like strata of obsidian or even, as he looked more closely, polished coal. Was that what they were on their way to do? Will's head immediately filled with images of miners stripped to the waist, crawling into narrow seams and hacking away at the dusty black coal face. His mind swam with apprehension.

After a few minutes they crossed through into a cavern, smaller than the one they had just left. The first thing Will noticed was that the air was different in here; the humidity had increased to the point that he could feel the moisture collect on his face and mingle with his sweat. Then he noticed that the cavern walls were shored up with huge slabs of limestone. Cal had told him that the Colony was made up of an interlinking series of chambers, some naturally formed and others, like this one, man-made with partially reinforced walls.

"I hope Dad's seen this!" Will said under his breath, longing to stop and savor his surroundings, perhaps even to do a sketch or two to record it. But he had to be content with taking in as much as he could as they tramped quickly along.

There were fewer buildings in this cavern, giving it an almost rural feel, and a little farther on they marched by some oak-beamed barns and single-story houses like little bungalows, some freestanding but most built into the walls. As for the residents of the cavern, he saw only a handful of people carrying bulky canvas bags on their backs or pushing loaded wheelbarrows.

The troop followed Mr. Tonypandy as he veered off the road and down into a deep trench, the bottom of which was full of sodden clay. Slippery and treacherous, it clung to their boots, hampering their progress as they weaved their way through a meandering course. Soon the trench opened into a sizable crater at the base of the cavern wall itself, and the work party drew up beside two crude stone-built structures with flat roofs. The boys seemed to know that they should just wait, leaning against their shovels and pitch cleavers as Mr. Tonypandy began a lively discussion with two older men who had emerged from one of the buildings. The boys in the troop joked and chatted noisily together, sometimes giving Will sidelong glances as he stood apart from them. Then Mr. Tonypandy left, limping off in the direction of the road, and one of the older men shouted over at Will.

"You're with me, Jerome. Go to the huts."

The man had a livid red scar in the shape of a crescent across his face. It began just above his mouth and ran up across his left eye and forehead, parting the man's snow-white hair and ending somewhere at the back of his head. But for Will, the man's eye, permanently weeping and shot through with a mottled cloudiness, was the most distressing aspect of his appearance. The eyelid over it was so torn and ragged that each time the man blinked, it was like a defective windshield wiper struggling to function.

"In there! In there!" he barked as Will failed to acknowledge the order.

"Sorry," Will answered quickly. Then he and two other youngsters followed the scar man into the nearest building.

The interior was dank and, except for some equipment in the corner, appeared to be empty. They stood idly around as the scar man kicked at the dirt floor as if looking for something he'd lost. He began to swear wildly under his breath until his boot finally struck something solid. It was as metal ring. He pulled at it with both hands, and there was a loud creaking as a steel plate lifted to reveal an opening three feet square.

"OK, down we go."

One by one they filed down a wet, rusty stepladder, and once they had all reached the bottom, the scar man took the lantern from his belt and played it around the brick-lined tunnel. It wasn't quite high enough to stand up in and, judging by the state of the masonry, was clearly eroded and badly in need of repointing where the chalky mortar had crumbled away. Will guessed that it must have been in use for decades, if not centuries.

Five inches or so of brackish water stood in the bottom of the tunnel, and it wasn't long before it plunged over the tops of Will's boots as he tagged behind the others. They had sloshed along for about ten minutes when the scar man stopped and turned to them again.

"Under here…" The man spoke condescendingly to Will while the others watched. It was as if he were explaining something to a young child. "…are boreholes. We remove the sediment… we unblock them. Yes?"

The scar man swung the lantern to illuminate the tunnel floor, which was heavily silted with little aggregations of flint and limestone shards rising out of the water. He slipped several coils of rope off his shoulder, and Will watched as each boy in turn took an end from him and tied it securely around his waist. The scar man tied the other end of each rope around himself, so that they were connected like a group of mountaineers.

"Topsoiler," the scar man snarled, "we tie the rope around ourselves… we tie it well." Will didn't dare to question why as he took the rope and looped it around his waist, knotting it as best he could. As he tugged at it to test it, the man held out a battered pitch cleaver for him.

"Now we dig."

The two boys began to hack away at the floor of the tunnel, and Will knew he was meant to do likewise. Probing with the unfamiliar tool, he edged his way along the brick lining under the swilling waters until he came to a softer patch of compacted sediment and stones. He hesitated, glancing at the other boys to reassure himself he was doing the right thing.

"We keep digging, we don't stop," the scar man shouted as he shone the lantern on Will, who immediately began to dig. It was hard going, both because of the cramped conditions and because the tool he was using, the pitch cleaver, was unfamiliar. And the job wasn't made any easier by the water, which, however fast he worked, would keep washing back into the deepening hole after every stroke.

It wasn't long before Will had come to grips with this new tool and mastered his technique. Now well into his stride, it felt good just to be digging again, and all of his worries seemed to be forgotten, even if only for a short while, as he threw load after load of stone and sopping soil out of the hole. With the water rushing in after every scoopful, he was soon thigh-deep in the borehole, and the other boys had to work furiously just to keep up with him. Then, with a bone-shaking judder, his pitch-cleaver jarred against something immovable.

"We dig around it!" the scar man snapped.

With sweat running down his dirty face and stinging his eyes, Will glanced at the scar man and then back at the water lapping against his oilskins, trying to work out the reason for their task. He knew he'd get short shrift from the scar man if he asked, but his curiosity was getting the better of him. He was just looking up to pose a question when there was an urgent cry, cut off almost as soon as it started.

"BRACE!" the scar man screamed.

Will turned just in time to see one of the other boys completely vanish with a loud gurgling as the water gushed down into what now looked like a huge drain the size of a manhole. The rope yanked tight, cutting into Will's waist and jerking with the fallen boy's desperate movements. The scar man leaned back and dug his boots into the grit and debris of the tunnel floor. Will found he was pinned to the edge of his borehole.