Nat strained his ears. He couldn’t hear anything, apart from the plink plink of water as it dripped from the roof.

“Come on,” said Woody. “We need to get out of here.”

“Wait a minute,” said Nat, a hysterical bubble of laughter in his voice, “haven’t you forgotten something?”

“Don’t think so,” said Woody, puzzled.

Nat felt around for his rucksack, opened it, and rummaged inside. “Here,” he said, “you might want these!” It was a pair of shorts and a T-shirt.

Nat relied on Woody to lead the way again. Although the phosphorus gave them some light, the bottom of the cave was strewn with slippery shingles, which made keeping their balance difficult. Nat was slipping and sliding on the loose scree, swearing to himself every time he slipped. He already had plenty of cuts and bruises from his flight through the woods and his struggle with the werewolf; he didn’t want to add to his injuries.

It felt like they walked for hours; their arms and legs were stiff with tiredness and their heads bent at awkward angles from trying not to bang them on the ceiling. But at last the tunnel opened up, and a patch of welcome light was visible up ahead.

“Look!” said Nat in relief. “There’s the way out.”

“Not daylight,” said Woody. “Don’t get too excited; it’s dark, remember?”

Woody was right. As they turned the corner the passage lost its greeny glow from the phosphorus and was lit by utilitarian halogens, like you would see in a factory or school. It had a dirt floor, on which stood various boxes and pieces of old office furniture.

“It looks like some sort of storage space,” whispered Nat nervously.

Woody nodded. “This is the bottom level; another two above us.”

“There’s our way out!” said Nat, pointing to a door set in the roughly hewn rock. It was a heavy iron slab, with a window in the center. Nat tried to peer through to see what was on the other side, but it had been blacked out. He pushed it experimentally.

To their surprise it swung open on silent, well-oiled hinges. Bravely, Woody peered around the door to see what was on the other side. It was another corridor, lit with the same harsh lighting, and with many other doors set within the rock, all closed. Nat pushed open the nearest one and they both stepped inside. There was no one else in the large room — no one else alive, that was.