Smouldering ash and a few fine threads of charred black material.

That was all that was left of Karugon and the two rucksacks. They had been completely obliterated as the entire cave trembled from the explosion. The blast had been powerful enough to punch a sizeable hole in the lower half of the spaceship stood just a few meters away. Rocks had dislodged from the roof, creating new dents in the roof as they plummet down upon the craft.

How could Peter have caused so much destruction with a single bullet?

"W-what… What the hell!?" Rose exclaimed. "What just happened?"

She was far away enough not to have been thrown to the ground, but her ears were still ringing. Her voice sounded muffled and distorted as though it was miles away from her body. Stefan's response was just as inaudible, but Rose caught snippets and mostly understood what he was trying to tell her and the Doctor.

"Grenades…" He explained. "Peter… a few… his pack. Just… a precaution."

"That's one way of putting it." The Doctor stated. "Come on."

Peter had been knocked off his feet, but he had sat back up by the time they reached him.

There were fresh trails of blood dribbling down from his ears. He was swaying slightly, dizzy and unfocused as he slowly came back around to his surroundings again.

"Hang on, stay still," Stefan told him. "Let me look."

Gently, he took hold of Peter's head and guided it in line with his. Holding up a single finger the corporal then began to move the digit back and forth as Peter obediently followed with his eyes. Able to do this without issue, he did wince when Stefan moved his head in each direction so that he could examine his friend's bloodied ears.

A few clicks of his fingers next to each of them told the soldier that Peter had not gone deaf as he reacted to the sharp sound both times.

"I'm fine." Peter insisted. "Just forgot how loud those things are."

"Yes, well it would have been nice to have had a little warning," Stefan remarked. "You're supposed to do that before you use them, Peter."

"Eh... No harm done."

"Try telling that to Karugon and all of our equipment."

Peter grinned back at his friend and shrugged apologetically.

"Collateral damage in an otherwise successful mission."

CRACK!

Already weakened by the creature's excessive digging, the remaining structure of the cavern was not as stable as it appeared to be and the shockwaves caused by the explosion had been too much for it. A boulder the size of a house came hurtling down and landed right on top of the spaceship.

Tearing through the metal framework as though it were made of tinfoil, the craft was bent and twisted beyond all recognition.

A huge cascading flow of water then came surging in from above.

"Where is that coming from!?" Stefan exclaimed. "We're underground!"

Peter swore very loudly as he remembered what he had been told about their location.

"We're also standing under a river," Peter informed everyone. "Kalagan said that's why they didn't dig straight up from here."

Stefan rounded on his friend, suddenly angry at him for this withheld piece of information.

"What, and you didn't think to mention that!?" He shouted over the noise of the gushing water. "You just set off several grenades, Peter!"

"I know I did!" Peter yelled back. "But funnily enough I wasn't planning on doing it!"

"That's enough." The Doctor intervened. "We need to get out of here, right now."

No one disagreed with him on this.

The river would eventually run dry, but there was potentially miles and miles of water about to pour down onto them. At best they would become trapped in the cave and freeze in the icy waters, and at worst it would go above their heads and leave them all treading water for as long as they could before fatigue set in and they would drown.

No rescue would come on time. UNIT wouldn't even know where to start looking.

"Stefan, grab that torch and guide us out," Peter ordered. "I'll take Jane and bring up the rear. Doctor and Rose, you stay between us at all times."

Grabbing one of the torches that had been left abandoned on the ground, Stefan made sure it was working before rejoining the Doctor and Rose as Peter sprinted over to where Jane had been put down. Incredibly, she was still unconscious after all this time.

It was probably for the best, Peter thought.

Hoisting her up and draping the woman over his shoulder, he stumbled slightly as the ground underfoot shook. More and more of the roof was breaking away, allowing even greater volumes of the river to pour in. Within minutes it would be reaching their ankles.

Then the unthinkable happened.

"Get back!" The Doctor shouted. "Stefan, stop!"

The Time Lord caught hold on the soldier's arm and pulled him back in the nick of time.

The tunnel leading back up the steep hill Peter and Stefan had fallen down was their only way out. The corporal had been about to lead them into it when the opening caved in on itself, large boulders stacking up until there was not even the smallest of gaps in which to get through.

"We'll shift the boulders." Peter quickly decided. "Here, help me put her down."

Between him and Stefan, they managed to sit Jane up against the wall next to the tunnel.

The two soldiers and Rose all then tried to create a way through. But it quickly proved impossible, and it was Stefan who became the first to realise the futility in continuing any longer.

"Even if we get through here, the whole network could have become unstable." He reasoned. "We can't risk going into an enclosed space. There could be another cave in and we'd get buried."

Rose had never thought that water could be so loud. The sheer volume that was now gushing in from the surface above was truly staggering. It was as though an entire ocean was rushing in to greet them. It had already reached every part of the cavern and was now on the rise.

"If we don't get out of here now." She shouted above it. "We're going to drown!"

But there was no way out. They were trapped.

Almost as though it were taunting them, a dim ray of sunlight could be seen poking through the waterfall. Creating a rainbow hue, it was illuminating the cave in a beautiful way that might have been admired had the cavern not posed the looming threat of becoming their tomb.

"No." Peter insisted, shaking his head. "No, we are not going to drown. We are going to get out of here, alive. There has to be a way!?"

But no solution came. No terrific thought or idea of brilliance manifested itself. Not for lack of trying or a will to live, but perhaps it was because there was no way out. They might die down here. The water level had already reached the tips of their heels.

A terrified shriek rang out and made them all jump.

Perhaps revived by the water as it seeped in through her trousers, Jane Wilson woke up in a complete panic. Yelling and kicking out wildly, the impact of her ordeal became obvious as she instantly tried to get up onto her feet and run away.

"No!" She screamed. "No, don't come near me!"

"It's alright," Rose told her. "You're safe. We're here to help you."

"No, you're all monsters!"

Weak and unsteady, the rising water did little to help Jane get a proper footing and she collided headlong into Peter. He barely moved as he caught hold of her and did not relinquish his grip even as she lashed out at him a few times to get away.

"Miss Wilson, listen to me." He said calmly. "Listen to me."

But Jane would not listen and was screaming now, fighting as though her life depended on it.

"No!" She sobbed. "You killed Tom. Y-your going t-to kill me, aren't you!?"

"I am most certainly not going to kill you." He replied. "My name is Peter Argent. I'm a lieutenant with the British army."

Jane had kicked him a few times and left a large scratch on his arm, the red marks vanishing almost instantly. But now the distressed woman's head was buried in his chest as she sobbed uncontrollably. Finally, she looked up at him.

"Y-your not...?" She tried to say. "You're..."

"I'm part of a team sent to rescue you," Peter told her. "Look, see?"

Rose gave a little wave as Jane looked her way.

"My name's Rose." She told her. "It's Jane, isn't it?"

"Yes," she whispered. "I'm..."

Words dissolved into more sobs as she began to cry again. Stepping away from Peter, she buried her face in her hands. Wasting no time, Rose waded over her and wrapped her up in her arms as she began to reassure her that she had nothing to worry about anymore.

"It's okay." She told her. "Shush, you're safe."

But although the cave had stopped collapsing in on itself, the water level was continuing to rise. It was now on its way up towards their calves.

"We are far from safe," Peter growled. "Doctor, what the hell are you doing over there?"

The Time Lord was stood where the edge of the large pool of water had once been. It was concealed now because of the rising water, but he had carefully navigated his way over to its boundary and was looking between it and the collapsed roof above.

"Do you see that?" He asked, pointing up. "There's sunlight."

"Sun would have come up about an hour ago." Stefan pointed out. "Why is that important?"

The Doctor smiled with confidence.

"Because sunlight means there's a way out of here." He replied. "Come over here and look at this."

Puzzled by the Time Lord's optimism, everyone obeyed and navigated their way over to him.

"If you're suggesting that we climb up there, Doctor?" Peter growled. "Otherwise how are we getting out of here?"

"O ye of little faith, Peter Argent." He chastised. "That would be ridiculous. No, our way out is down there."

He pointed down at the surface of the water straight in front of him.

From this angle, it was possible to see the different hues of the water as it grew darker and murkier the deeper it went. But somewhere deep below was a small, isolated patch of a lighter colour that seemed to have captured some of the sunlight's reflection.

"It's just the sun bouncing off it." Stefan decided. "A trick of the light."

"No, it's not." Peter disagreed. "It's too deep and the sun rises in the East. It's pointing the other way."

He was right. The bright ray of sunlight was illuminating the remains of the spaceship and the wall behind it, the golden light was nowhere near the pool of water and couldn't be causing the shimmering patch they could all see.

"I thought the air was cooler in here," Rose remembered. "That's because there's another way out!"

The Doctor beamed at her.

"You noticed straight away." He praised. "The only problem is that it's underwater."

Those torn away parts of the spaceship that were light enough to float had begun to bob around the cave, scraps of debris and scraps of metal being tossed around as the water continued to rise.

"We'll just have to swim through it," Peter announced. "We've got the torch and… Well, we have my eyes too. We can do it."

Jane was still holding on tightly to Rose's hand. Trembling from head to foot, she didn't look best pleased with the idea of undertaking such a dangerous means of escape.

"W-what if we g-get lost?" She protested. "We'll drown!"

"We'll drown if we stay here." Peter countered. "Look, I'll go first and come back. Either there's a way out or there isn't."

"Peter, we don't have a guide rope," Stefan told him. "If you get stuck or lost down there on you're own..."

He didn't have to speak of the consequences. Divers always went in pairs, and they had the luxury of oxygen and other navigational equipment. Peter only had his lungs and a determination to survive.

"I know, but we don't have a choice."

Unclipping the radio from his belt, Peter also removed his gun and its sheath. Such bulky items were not needed and could catch against something if his route out was as tight as he was imagining it was going to be.

The lieutenant handed them both over to the Doctor.

The Time Lord took the radio but hesitated over accepting the weapon from him.

"Oh, I don't like guns." He moaned. "Really, I don't."

"Well, you're going to have to look after this one," Peter told him, thrusting the weapon into his hands. "At least until I get back."

It was how he said it that made the Doctor accept the gun. There was a hint of fear in the younger man's voice which spoke of the risk he was about to take. A great deal of self-confidence was required, along with a level of bravery few possessed.

"Good luck, lieutenant." He told him.

Peter responded with a nod before he turned back to face the large pool of water. He didn't know how far the tunnel went on for, or if it was even passable. But there was sunlight, and that was motivation enough for the moment.

"Peter, this is ridiculous." Stefan protested. "At least let me go down with you."

Peter smiled at his friend. It was typical of Stefan to want to be at his side, ensuring whatever dumb plan was running through his head went off without issue and ended up working out as intended.

"No, one of us needs to stay up here." He said. "Besides, better me than you. Emma would kill me otherwise."

"She'd kill us both," Stefan responded. "But I guess there's no stopping you."

"No, there isn't. Wish me luck."

Not trusting himself to delay the inevitable any longer, Peter sprang forward and dived headfirst into the water.

At first, he could see nothing but a swirling cycle of bubbles as the world above him vanished, taken over by the darkness of the water. Then, as though someone had lifted back the curtain, he was able to make sense of his new surroundings.

Above him was lighter and below was pitch black save for the singular patch of light he was aiming for. Simple enough perhaps, but lifesaving as far as he was concerned. One of the main causes of drowning was people becoming disorientated and not knowing which direction to swim for.

At least the coldness of the water wouldn't be a problem.

Being what he was, Peter had discovered that after his first transformation he had begun to function with a slightly higher body temperature. As a result, he was far less susceptible to the cold than humans were and was grateful for this side effect right now.

The cold would slow him down, sap his strength and force the oxygen out of his lungs more quickly as the pressure on his chest grew with every passing moment he spent underwater.

Still, Peter could not hold his breath forever. Although he was protected from the freezing waters, it did not exclude him from having a limited lung capacity.

He continued to swim down, towards the ray of sunshine that was their only hope of survival. As he neared it, the wall of the cavern loomed out of the darkness to greet him and he could now see where it was he needed to head towards.

The entrance was circular, like a gaping mouth. This impression was heightened when Peter swam closer and looked inside. The cave hadn't always been underwater and, over a period of time that must have been in the thousands of years, stalactites and stalagmites had grown.

Peter could not remember which was which as he stared at the needle-sharp spears that were hanging down from the ceiling and protruding up from the floor.

But even at this distance, something was menacing about the cave that gave him the chills, even if the water could not. It was like looking into the open mouth of some giant, undersea monster. He could almost imagine the stalactites and stalagmites biting down, the whole thing swallowing him up.

But he had to go in. People were going to die otherwise.

From the moment Peter had vanished below the surface, Stefan had begun to time how long it was he had been gone. Announcing every minute that passed without any sign of his friend's return, the corporal had grown ever the more agitated.

"Three minutes." He had announced, consulting his watch. "Three minutes and counting."

"Is Peter a good swimmer?" Rose dared to ask. "How long can he hold his breath for?"

"Yeah, he's pretty good. If anyone can find a way though it's him."

Rose noticed that he had avoided her second question. But she couldn't blame him for doing so, not when the thought of Peter not making it back was such a daunting prospect.

She shuddered at such a grim thought.

"Most humans can hold their breath for a minute, maybe two." The Doctor said. "But I think with enough practice and a good deal of fitness, there's no reason why that can't be extended to five or six…. Eight or nine is even possible, yes."

"Is Peter any different?" Stefan question suddenly. "What he is, does the make a difference?"

The Doctor shook his head.

"I don't know, I'm sorry." He said sincerely. "Might be the same, might be more. Might be less."

Jane might have found this strange had it not been for the fact that the water level was now up to their knees. She couldn't even fathom how a weekend getaway had resulted in any of it. Aliens, an underground labyrinth and people who seemed to take it all in their stride… She just wanted to be back home.

"H-he seems s-strong." She stuttered. "I think he'll m-make it."

"He will, Jane," Stefan told her as he checked his watch again. "He has to. Four minutes. Come on, Peter."

The next three minutes passed very quickly, and after that, it seemed each one dragged by deliberately slow in order to torture them as much as possible. Peter did not resurface even after the ten-minute mark came and went. Eleven minutes… Twelve minutes… Thirteen…

Time passed them by with a deafening silence.

The Doctor's maximum estimate of the lieutenant's lung capacity was now relying on Peter now being on his return journey. Any longer meant that he had run into difficulties, that he had become lost or stuck and he would not be coming back at all.

The reality of this was weighing heavily on Stefan as he continued to count the seconds as they ticked by.

"Maybe he stopped at the surface?" Rose suggested. "Just to catch his breath before he came back."

Stefan shook his head.

"Peter wouldn't linger." He said. "Not when he knows we're in danger. Fourteen minutes…"

"I could be wrong." The Doctor admitted. "Peter will be fine."

"What if he isn't? What then!?"

It was a rare slip of composure for Stefan. He was a military man, used to keeping calm even under the highest of pressured of situations. But the thought of losing his best friend to such a horrendous fate was beginning to seep into any sense of optimism that was left.

For once the Doctor had no answer to give.

The water was up to their hips now. Soon they would no longer be able to remain standing up and would have to begin treading water. But even if they did, there was nowhere for them to swim to and they would quickly tire and slip below the icy water.

"Well, I think he can do it," Rose said, more loudly than she had intended. "Come on, Stefan. You've known him how long?"

"Seventeen years." The corporal acknowledged with a faint smile. "We met on our first day of school."

"Exactly, and how many time has he let you down since then?"

Stefan knew the point she was trying to make and nodded at her, grateful for the sudden surge of confidence.

"You're right, Rose." He said. "Peter's too stubborn, too damn determined to let any of this stop him. He's a tough sod, I'll give him that. I known shouldn't worry but…"

"He's your friend." The Doctor said. "You care about him, that's all."

Shivering as the churning water reached her stomach, Rose found herself laughing at a very sudden thought.

"He's kind of like you, Doctor." She teased. "Waits until that last possible minute and then races in and saves the day like it's nothing at all."

Though the Time Lord frowned at this, the analogy amused Stefan greatly.

"Careful Rose, that's a dangerous comparison." He chuckled. "Don't let Peter hear you say that."

"Oi!" The Doctor whined. "I'm not that bad!"

But he was glad to see that the corporal was in a slightly brighter mood. Despite their desperate situation, he had stopped counting now. Not that it even mattered any more as Peter would either be back or he wouldn't be. Even Jane let out a faint, wheezing giggle.

The infectious laugher lingered even as Peter burst through the surface.