Tunnels 01, Tunnels

replied thoughtfully, still grinding it. "Yes, I'm pretty sure this is limestone... You see, it breaks down into a smooth paste... If it was sandstone, it'd be crunchier, and even squeak a little as I bit it."
    Chester winced as he heard the sounds coming from his friend's mouth. "Are you serious? Doesn't that crack your teeth?"
    "Hasn't yet." Will grinned. He reached into his mouth to reposition the flake and chewed on it for a little longer. "Definitely limestone," he finally decreed, spitting out what was left of the flake of rock. "Want a taste?"
    "No, I'm fine, really," Chester replied without a moment's hesitation. "Thanks anyway."
    Will waved his hand in the direction of the roof over the cave-in. "I don't believe there'd be a deposit -- an isolated pocket of limestone -- anywhere near here. I know the geology of this area pretty well."
    "So what are you getting at?" Chester asked with a frown. "Someone came down here and blocked up the tunnel with all this stuff?"
    "Yes... no... oh, I don't know," Will said, kicking the edge of the huge heap in frustration. "All I do know is that there's something very funny about all this."
    "It might've been one of the gangs. Could it be the Clan?" Chester suggested, adding, "Or maybe even the Click?"
    "No, that's not likely," Will said, turning to survey the tunnel behind him. "There'd be other signs that they'd been here. And why would they just block up this tunnel? You know what they're like -- they would've wrecked the whole excavation. No, it doesn't make sense," he said, bemused.
    "No," Chester echoed.
    "But whoever it was, they really didn't want us to go back in there, did they?"

    * * * * *

    Rebecca was in the kitchen doing her homework when Will returned home. He was just slotting his shovel into the umbrella stand and hanging his yellow hard hat on the end of it when she called to him from around the corner.
    "You're back early."
    "Yeah, we had some trouble in one of the tunnels and I couldn't be bothered to do any digging," he said as he slumped down dejectedly in the chair on the opposite side of the table.
    "No digging?" Rebecca said with mock concern. "Things must be worse than I thought!"
    "We had a roof fall in."
    "Oh, right...," she said remotely.
    "I can't figure out what happened. It couldn't be seepage, and the really odd thing was that the infill...," he trailed off as Rebecca rose from the table and busied herself at the kitchen sink, clearly not listening to a word he was saying. This didn't bother Will unduly; he was used to being ignored. He wearily rested his head in his hands for a moment, but then raised it with a start as something occurred to him.
    "You don't think he's in trouble down there, do you?" he said.
    "Who?" Rebecca asked as she rinsed out a saucepan.
    "Dad. Because it's been so quiet, we've all assumed he's gone somewhere, but he could still be in the cellar. If he hasn't eaten for two whole days, he might have collapsed." Will rose from his chair. "I'm going to take a look," he said decisively to Rebecca's back.
    "Can't do that. No way," she said, spinning around to face him. "You know he doesn't let us go down there without him."
    "I'm going to get the spare key." With that, Will hurried out of the room, leaving Rebecca standing by the sink, clenching and unclenching her fists in her yellow rubber gloves.
    He reappeared seconds later. "Well, are you coming or not?"
    Rebecca made no move to follow him, turning her head to look out the kitchen window as if mulling something over.
    "Come on!" A flash of anger suffused Will's face.
    "Fine... whatever," she agreed as she seemed to come to again, snapping off her gloves and placing them very precisely on the drainer at the side of the sink.
    They went to the cellar door and unlocked it very quietly, so their mother wouldn't hear. They didn't need to worry, though, since the sound of a barrage of gunfire was coming thick and fast from inside the living room.
    Will turned on the light and they descended the varnished oak stairs he had helped his father fix into place. As they stood on the gray-painted concrete floor, they both looked around in silence. There was no sign of Dr. Burrows. The room was crammed with his belongings, but nothing was that different from the last time Will had seen it. His father's extensive library covered two walls, and on another were shelves housing his "personal" finds, including a railwayman's lamp, the ticket machine from the disused railway station, and