The Doctor really didn't have a choice but to leave Josh where he was. If there were others alive within the storm drains then he had to try and get them out as well. He aimed the sonic screwdriver ahead of him as he walked along the tunnel. Just a few metres further along the light of sonic picked up fluid splattered up the side. In the blue shine it looked black, but the Doctor knew it was red. He could taste the tang of copper in the air. It was blood, most likely human blood, and there was a lot of it. Beneath the smell of fresh blood there was more, the rotten stench of decay, and as he moved cautiously along the tunnel it was getting stronger.
His hearts were battering in his chest as he tried to keep his wits about him. He felt surrounded by the terror making his head ache. There was still someone within the tunnels who was terrified. Someone who was strong. They were stronger than a human, but not wild like an animal. It was something else. Something new. It was impossible to pinpoint or to track. Even though he was heading down into the darkness and nothing had passed him, he got the hint that it was behind him, he kept wanting to spin round and see what was following him, but he knew if he did there would be nothing there. He wasn't used to feeling this anxious or vulnerable. He wanted to run, but he pushed on forward, round the bend in the tunnel and into a junction. The tunnel split into three and it looked like the concrete in one of the tunnels was morphing into limestone. He scanned the area. The tunnel to the right linked to a natural cave system.
He could see drag marks in the damp mud in the base of the central tunnel and what looked like a three toed footprint. Whatever made it wasn't a dog or a wolf, the toes were long, pointed, and spread out with fearsome claws. He was reminded of the fossil prints of a velociraptor he'd helped to uncover some years back. Whatever it was down there with them, at least it couldn't be a velociraptor - could it?
The Doctor scanned the tunnel with sonic. It looked like this tunnel also spread out into caves. He continued cautiously on. Just beyond a sharp turn and a blood covered rock he found the body of a teenager. He was dead. The Doctor didn't have to use sonic or check for a pulse to make sure. Deep claw marks slashed through the remnants of a black T-shirt. They split his abdomen open, spilling glossy rolls of intestines into the dirt. His throat and half of his face was torn into a gruesome pulp of bloody tissues and smashed bone. His remaining eye was open, staring unseeing up at the Doctor. "I'm sorry."
The Doctor stepped over him, trying not to stand in blood that had spilled out along with his innards. The stench of decay was growing stronger as the Doctor slowly picked his way from the concrete of tunnel and into the narrow entrance of a natural limestone cave. He passed easily through the vertical cave entrance and stepped up onto a ledge. The cave opened wider and the base of it was over a metre below him. He scanned the cave. There were mounds of limestone growing up from the base as water dripped down from above. He could hear several points of steady dripping within the cave, as yesterday's rain made it's way down through the rocks above, but there was something else in there with him. He paused and stood perfectly still, holding his own breath, as he thought he heard movement. He tried to focus past the sound of his rapid heartbeats and the patter of dripping water. He had to get himself under control. He heard it again. Something shuffled. He heard shallow laboured breathing and a quiet whimper. The Doctor dropped down into the cave, his converse skidded and he almost fell as he landed. He shone the sonic down and grimaced at the mess of flesh he'd just stood on. It wasn't new. It was a scrap of dark and rotted sinew which had been discarded some time ago.
The Doctor hugged the side of the cave, keeping his shape as small as possible, moving slowly and making sure he didn't draw attention to himself. He narrowed the beam of light produced by sonic so it only lit the rock by his feet. The soft buzz of his screwdriver sounded deafening in the otherwise dark cave. He heard the shuffling again. It was coming from beyond a bulge in the rocks. He heard a desperate moan. It wasn't an animal. The Doctor leapt forward and down to his knees beside another teenager. The track of his movement across the floor of the cave was marked by a broad trail of blood. His right leg was missing. Twisted and ripped flesh hung where his knee should have been. It was clear his leg had been ripped away rather than cleanly cut or bitten.
"Help me?" the teenager's groaned plea gurgled in the back of his throat as the Doctor put his hands on him.
"Shhh, I've got you," the Doctor soothed. He felt into his neck for a pulse. His breathing was rasped and rapid, his pulse faint and unsteady. There wasn't enough blood left in his veins. Even if he picked him up and ran with him he'd not get him beyond the cave back into the storm drain never mind to the TARDIS. The Doctor carefully eased him over.
"Green Day?" he asked him gently only just able to decipher the remnants of a logo on his tattered and bloody shirt. "Is that a band?" Four long slashes striped his reddened jeans, shredding his thighs to bone. He whimpered as the Doctor eased him up slightly into his lap. "It's going to be okay," the Doctor whispered as he ran his hand over his head. He let his fingers drift to the side of his muddy face. "You're okay," the Doctor insisted. The terror and fear lining the teenager's face calmed.
"The kid…" he breathed. "…is he?"
"He'll be okay," the Doctor soothed. "I'm going to get him out."
"I'm sorry… didn't mean…"
"Shhh, it's okay." The Doctor held his hand and caressed his head as his ragged breathing became more staccato. He tried to pour peace into him as the teenager slipped away in his lap. The Doctor gently lowered him to the cave floor. Whatever was in there with them, whatever that animal was; it was ripping people apart. Ripping children apart. The Doctor rose to his feet and straightened, anger nipping at the psychic fears that still enveloped him. He headed deeper into the cave system, following the intensifying reek of death and decay.
There were bloody drag marks leading to what looked like a larger, deeper, underground cavern. The Doctor crouched at the entrance. The smell that rose from the area was close to overpowering. He shone the sonic down to illuminate bodies in various states of degradation. They were laid in a jumbled mess of part eaten, smashed, slashed, dismembered bodies. What looked like fresher bodies were around the edges with rotting carcasses in the centre. They weren't all human. It looked like there was cows, pigs, sheep, and he thought he could make up the hind quarters of a shredded horse, all rotting together in a jumbled mulch of death.
A movement caught his eye. Crouched down at the far edge of the cavern was an animal. As Josh had told him it was big. It was big dog sized, but it certainly wasn't canine. Plates and spines ran down its scaled furless back, its spine continued into a powerful looking whip-like tail. Its snout was elongated and filled with curved teeth. Four front teeth extended beyond its snout in hooked fangs. It was feeding, burying its nose into a belly wound through a T-shirt that was now almost entirely red. A few patches of yellow on the collar the only sign of the original colour. The Doctor held his breath watching with sickened fascination. He'd never seen an animal with that body pattern before. It certainly wasn't from Earth, but it didn't strike him as being an intelligent space-faring alien species either.
He was so focused on the animal feeding he jumped when a second leapt down from a ledge at the back of the cave. It snapped and snarled at the feeding animal which snarled back, but then bowed its head and moved away from their fresh meal. The second creature took its place grabbing the victims arm. The second creature angled its head to the side, using teeth further back in its head to crunch through the bone.
The Doctor could hear the crushing and splintering of the humerus bone within its jaws. He looked up to the ledge. A third creature was lazily getting up and yawning. There were several more sprawled out and sleeping across the ledge. Was that six of them? No, seven? No, there were eight. There were eight of the creatures within the cave. The Doctor scanned the cave itself, looking to see if there were any other entrances or exits and he picked up another tunnel on the far side. He wasn't going to be able to get to it from where he was. He moved slowly, but they didn't react to the light of sonic or the gentle buzz.
He needed to get back to the TARDIS. He needed to figure out what they were. Where they had come from and what he was going to do about them. He could see no intelligence in them beyond the instinct to hunt, kill, and eat. Maybe there was a hierarchy within the group with the first one he'd seen deferring to the second over a fresh kill, but there was certainly enough food in the cavern to support eight animals. It was likely they would drag the other two he'd found dead into their larder to let them rot and decay as well. He wasn't going to be able to afford the time to bring the dead out. Not until he'd figured out what to do about the animals. There was also Josh to think about.
Without taking his eyes off the creatures in the cavern the Doctor backed away again. He got to the point where he was out of sight and he hoped out of earshot from the creatures and then he turned and ran. He hoped they were too busy feeding and relaxing to come after him. As he passed from the cave and back into the manmade tunnels he almost tripped over a discarded rucksack. He picked it up and shouldered it, before continuing to run along the tunnel to where he had left Josh. There was a small plastic bag still containing three bright blue pills on the ground but there was no sign of the boy. He'd gone.