Tunnels 03, Freefall

chimney pots simply exploded, pieces of it raining all over him.
    "What the hell?" Dr. Burrows spluttered, and flung himself down with his arms around his head. He didn't stay down for long, immediately scrambling back over the roof and scattering fragments of the red chimney pot as he went.
    Drake raced to the rear of the roof where he checked the alleyway behind. "Keep low and stay close," he ordered Will and his father as he scrambled over the brick parapet to reach the adjoining roof.
    "Are you telling me we were just shot at?" Dr. Burrows asked, wiping dust from his face.
    "Yes, you gave our position away. Can't you ever do what you're told, Dad?" Will said in an exasperated voice as he followed Drake.
    Crouching and in single file, they continued to cross from roof to roof as they made their way along the line of houses.
    "But I didn't hear any shots," Dr. Burrows whispered as they went.
    "They'll be using silencers or some kind of suppressor, and maybe low-velocity ammunition," Will said.
    "Go to the top of the class, Will. You really have mugged up on your military manuals, haven't you?" Drake smiled. As they came to the last house in the terrace, Drake crawled forward on his chest and heaved up a hatch in the roof. He swung himself through the opening, crashing into some old cardboard boxes in the attic below. Will and Dr. Burrows dropped in after him.
    "So what do we do now?" The whole block will be surrounded," Will asked, looking quickly around at the empty attic, identical to the one they'd been in before, as he imagined an army of Styx and Colonists taking up positions outside.
    Drake flicked a small torch on. Gripping it in his teeth, he went to where the chimney flues ran up the wall and began to tap the brickwork. "Never get yourself into any situation where you haven't got at least two escape strategies," he said from the corner of his mouth as he worked his way along the wall. Although there was no difference in the appearance of the brickwork, the sound changed -- it became hollow, as if the wall was made of metal. He pushed against it and a small trapdoor swung inwards. Will and Dr. Burrows were beside him in an instant, peering down into the duct. Inside it a rusted metal ladder was bolted to the wall.
    Will was relieved they had a way out. "That's a really cool escape strategy!"
    "Yes. Thanks to Martineau," Drake said.
    "Sir Gabriel Martineau?" Dr. Burrows asked.
    "Sure. He loved his secret passages, and got his men to build them on a whim. And he was usually in such a tearing hurry, he often didn't stop to make records."
    "So the Styx don't know about this one?" Will asked.
    "I truly hope not." Drake turned to Dr. Burrows. "And Doc, do you need any more convincing that the Styx are a threat?" he said pointedly to him. "Like a bullet in your head?"
    Dr. Burrows frowned, but said nothing.
    "Good. Now pick up your kit and get down the ladder -- and take a left at the bottom," Drake told them.
    Will and his father descended the old ladder, then began along the stone-lined passage, which was high enough that they could both stand. A small stream of brownish water trickled down the center of the passage, and its sides and roof were covered in glistening black slime. As they walked, the light from Dr. Burrows' luminescent orb revealed there was more to the walls than they had first noticed.
    "Look! A mural!" Will cried. "A man with a boat!"
    "Noah and the Ark, I'd say," Dr. Burrows proclaimed as he inspected the image under the garlands of black algae and pale smudges of limescale. "But they're not murals, they're carved in relief, cut into the stone."
    "And here's one of a man and a woman," Will said, squinting at the other side of the passage.
    "Adam and Eve, probably," Dr. Burrows said. "They're all Biblical scenes, sculpted into the limestone with such skill. The artistry is just breathtaking. Remarkable!"
    Drake seemed to be taking his time to close the trapdoor, but as he slid down the ladder and caught up with father and son, he found they were both so captivated by the murals that they had hardly gone any distance at all.
    "I told you two to make tracks!" he snarled.
    "But this is an important discovery," Dr. Burrows insisted. "Why on earth would anyone have put these down here?"
    Drake glanced warily down the passage behind them. "Three centuries ago this led back to Martineau's house, so he could walk to church without getting wet when it was raining." Drake took Dr. Burrows by the arm,