Charlie's heart was racing, and his head was pounding. He was one the verge of death. In extremis. He was going to die, and the only image invading his mind was that of Nate, staring down at him, worry plastered across his face. He was struggling to think clearly, and he knew that they had maybe seconds to live.

The circuit was complete. The final components – the Doctor and Charlie – were in place. Were they too late? Had he missed something else?

He felt a rush of adrenaline yank his mind back to the present.

He could see the energy coursing through the room. It was invisible, but there in his mind's eye.

Blue crackling waves of energy, burning like fire from the silver circuits.

They leapt across the stones, connected by the strips of metal – and even by the Doctor. He could see the fire arcing over him, where he stood as part of the room's circuitry.

The Doctor was engulfed in flames, but he was unaware of it. He was more concerned by the ceiling rolling down towards them.

His burning torch was extinguished, plunging them both into darkness.

There were voices whispering to him. Charlie wasn't sure if they were real, or just figments of his imagination. The Doctor didn't seem to hear it.

The Time Lord cannot see the burning. He cannot see the fire in your soul.

The energy was closing in on him. It jumped across the stone tracks, circling and spiralling towards him. He was at the centre, and it was going to hit him.

Show him the fire.

Show him the burning.

The whispering voices were multiplying – more and more voices adding to the panic in his mind.

Sssshhh….

The susurrations in his ear made his skin crawl. He couldn't quite hear the words, but he knew what it was saying.

This was the last room. There was no way through any of these walls.

But there was always a way out – the Doctor had taught him that.

The stone ceiling was coming down, eliminating any escape in front, behind, or above them. That left down. There had to be a way down.

Charlie's hand had made contact with the crystal embedded in the floor, at the centre of the circuit pattern.

As he removed his fingers, he saw that the gemstone was glowing. Something was happening. Some mechanism had been activated.

A grinding noise. Like a whetstone sharpening a sword, or an old smoker coughing up their lungs.

In a strange way, it reminded Charlie of the TARDIS engines; ancient, failing machinery – yet something which felt very much alive.

As the ceiling above them descended, so did the floor.

The stone slabs in their concentric circle pattern began to unravel beneath them, and the floor uncoiled into a spiral staircase, lowering the Doctor and Charlie to safety.

A flint-stone mechanism sparked flames into life, igniting a circle of torches recessed in the stone.

Finally, the grinding stones crunched to a halt. The ceiling settled in its new position. The room around them had transformed into a grand antechamber.

The Doctor stared at him.

"How did you do that?" he asked.

"I'm not sure."

"Well, that was a close call," the Doctor admitted, brushing the dust off his jacket. He offered Charlie an excited grin, as if the ordeal they had just experienced was more exhilarating than terrifying. "I thought we were dead for sure then. Well done."

A large archway had opened up in one the side of the chamber, ejecting them into another dimly lit chamber.

Around the archway were familiar carvings – more of the three-dimensional writing the Doctor had spotted before.

Charlie was buried in his thoughts, as the Doctor bounded up to the carvings, consulting the sonic screwdriver as he ran his fingers along the words.

"The sonic screwdriver's completed the translation," he half-mumbled an explanation, greatly fascinated by the findings rather than how he had managed it, "As much as it can, anyway."

Charlie wandered through, taking in the sight of a forged metal altar, blackened by the centuries.

The Doctor's voiced echoed into the room.

"This temple is dedicated to energy… life force… maybe power. Yes, power. A being of great power once resided here. It ruled over the people of the world, subduing them with fear… No, mind control…?"

As the Doctor spoke, Charlie was drawn to the effigies of giants attending the altar. Each a hulking beast with four arms, presenting a blue gemstone in their sculpted hands.

"There was a revolution. The power was lost."

The biggest statue of them all, a terrifying wrought iron image of a snake taking pride of place at the head of the room, froze Charlie to the spot. He was transfixed by its cold stare, its corroded fangs. The thing looked like it had been turned to stone mid-strike.

"But not… forever?" the Doctor finished. He sounded perplexed by the translation. Perhaps it was wrong, or missing an important word. Its message wasn't clear.

The buzzing of the sonic screwdriver told Charlie that the Doctor had joined him at the strange altar.

"The walls are reinforced," the Doctor concluded. "Deadlocked."

This didn't matter, Charlie decided. Whatever the Doctor was prattling about wasn't important.

"Those gemstones the statues are holding," the Doctor scanned them, casting a puzzled glare over the sculptures, "They're a barrier of some kind, focussing energy into the centre of this chamber."

What was important? Charlie's mind was whispering to him, now. What really mattered?

The Doctor whirled round, his disturbed gaze landing on the largest statue. His lips murmured words in silence.

The Doctor has that power. He can change time.

You've waited so long for this. You want this to happen.

"This isn't a temple…," the Doctor uttered, "It's a prison. All those puzzles, designed to stop just anyone breaking in."

You just have to let that desire in.

Let it in, and make everything better.

Charlie finally spoke. "You can change it."

His words were clear, strong. Not shy, or uncertain, like Charlie's voice usually was.

That distinction was enough to make the Doctor stop, turn around, and listen to him.

"You have that power." Charlie's head was spinning; his sudden revelation was intoxicating. "You have the power to change time!"

The Doctor raised an eyebrow; alert to Charlie's commanding tone.

"Is this why we're here, Charlie? Is this why you brought us here?" the Doctor asked, very carefully, his arms outstretched to calm him.

"You can change time," Charlie repeated.

The Doctor frowned. "We've talked about this, remember? The web of time is complicated. Every decision ever made is woven through time, setting it on its course. We can't just go back and change whatever we like."

"But you've done it before, haven't you? Changed time," Charlie insisted more aggressively.

"And I've damaged it." The Doctor blinked, struggling to choose the right words to reach Charlie with. "I simply can't change something in your past if it has any way resulted in you standing here, right now, saying these exact words. To do so would cause unimaginable damage to reality. It would break every rule I've ever lived by!"

"You save people all the time, but you won't do this because it 'breaks your rules?'" Charlie shouted, exasperated. "You're such a hypocrite! You have one rule for yourself and one rule for everyone else!"

The Doctor peered into the boy's eyes, which flicked away, avoiding his own. There was something there – a shine. A dangerous, manic glint, and it made his hearts twinge. Because he recognised it – madness. It was madness he'd seen in other eyes far more dangerous than Charlie's.

"This is about Nate," the Doctor realised.

"How… how do you know?"

The look of apprehension in the boy's face betrayed his surprise that the Doctor had started to uncover his secret.

"I didn't, but I do now," the Doctor admitted. "So that's what all of this has been about? That's why you came with me…?"

"You have to save him. That's what you do!" Charlie was almost begging. "You're the Doctor. You make everything better! That's what you're for!"

"No, Charlie, that's not…"

"You said you'd help me, Doctor. You promised!"

"I can't…"

Charlie's bottom lip began trembling uncontrollably.

He rubbed the back of his neck in agitation. The Doctor wasn't listening to him.

After everything the Doctor had said, after everything they'd been through… he wasn't going to help him. The Doctor always broke the rules for himself, or his friends – but not him.

That one thought made him furious. It wasn't fair!

Charlie's eyes were burning, and he was desperately trying not to cry, but that just made him angrier.

That serpent was leering over him, taunting him – daring him to make his move.

"I wasn't there for him, when he needed me. I didn't see it. And now he's dead." The words tumbled out, releasing all the emotion he'd kept boiling inside him for months.

He turned to the Doctor, his shoulders broad in an aggressive stance.

"Save him, Doctor. I will not let him die. I will not let Nate die!" he screamed.

The Doctor, astonished, looked at his friend: confused, angry and desperate.

No. This wasn't right.

"Charlie… stop," the Doctor commanded, levelly. "This isn't you."

As the Doctor stepped towards him, Charlie whipped something from his back pocket.

A knife. The blade gleamed in the light from the burning torches around the room.

Where the hell did he get that? The Doctor growled under his breath.

"Stay back!" Charlie warned.

The Doctor did not, and continued stepping cautiously towards him, his hands extended in an open gesture to show he meant the boy no harm.

"Or what? Are you going to kill me?"

Charlie shuddered; his face plastered with fury, but didn't respond.

"You know that won't do either of us any good," the Doctor spoke as kindly as he could.

Charlie's eyes flickered towards the stone floor, and the Doctor saw his chance. Before Charlie could react, he lunged, and grabbed the boy's wrist, twisting the blade from his fingers. It clattered to the floor.

The Doctor's gaze fell upon the cuts on Charlie's arm - zigzagging, exactly like a snake…

"But that's…!" the Doctor exclaimed.

He had seen a mark like that before – a long time ago.

"Charlie, that's-"

He didn't finish his exclamation, as Charlie swung a sloppy right hook at him, which the Doctor blocked easily.

With a cry of "Haik!" the Doctor knocked Charlie on his back, winding him.

Charlie gasped for breath, baring his teeth at the Doctor, almost hissing with fury.

"I'm sorry, I should have realised…" the Doctor backed away from Charlie – back the way they had come - as everything fell into place in the Doctor's mind. Every action Charlie had taken suddenly made sense.

"Charlie, listen to me…" the Doctor pleaded with him, as he saw the rage in the boy's eyes. It was a look of such malice, that the Doctor began to lose hope. Was Charlie still in control of his body? Of his mind? Or was something else?

"No, Doctor," spat Charlie, "you listen to me! We're-"

Charlie stopped. He jerked suddenly, as an incredible pain surged up his spine. He grasped at his hair. The Doctor could see that he was in agony.

All that violence was gone from him in an instant, transformed into some intangible force which was now lashing down upon him. Something was taking Charlie from him.

For Charlie, it felt like a blade was being twisted in his brain.

Something sliced its way through his mind, burning through his consciousness.

The pain was rending him in two. Nothing the Doctor said or did made it through to him.

He screamed, but his lungs were burning, and the sounds died in his throat.

The pain stopped, and Charlie looked at the Doctor, breathless, his eyes filled with fear. His legs buckled, and he toppled forwards.

The Doctor lunged for him, and caught him, grabbing his arms.

Charlie looked desperately into the Doctor's anxious old eyes, as the realisation of what he had just done became apparent to him. Oh god, he had just threatened the Doctor.

He tried to shake away the dream-like quality of the scene around him, but he couldn't. Maybe he was dreaming. He wasn't sure; his senses were deceiving him.

He focused on the Doctor's pupils, but he was too confused to concentrate properly. He needed the Doctor… just to make things better.

He sobbed. "Please help me."

The Doctor grimaced, his face a mask of horror, as Charlie tore away from him, his body thrashing and jerking wildly; possessed.

The boy's form seemed to be melting, transforming; his limbs shrivelling away, his neck elongating. His skin charred, the molecules of his being burning and morphing into something new.

The Doctor backed away, muttering in resentment.

A booming sound echoed around him, as a voice began to speak; deep, smooth, and feminine. "I am reborn, old man. My sacred temple has returned to me, and I am reborn, again!"

"No," the words of protest barely made it through the Doctor's throat, as he staggered backwards. The sounds he made were weak, fragile. Pathetic. "No!"

"This is my grave and my cradle. My prison and my freedom. Witness my rebirth, Doctor. Witness my return!"

Charlie was enveloped in a sudden vortex of atoms; black shapes swam together as he began to transform into the very shape the Doctor had feared: a serpent.

For he had encountered this entity before. Time and time again this creature reared its demonic head, turning temptation to chaos, dragging him and his friends through hell.

This thing was a legend, a myth, wielding unspeakable power. Its name:

"The Mara!" the words passed through the Doctor's lips in disbelief.

The newborn creature's eyes snapped open; yellow orbs slashed through the centre by a thin black pupil. The eyes glistened.

"Every child," it spoke, "throughout the cosmos will dream. And the dreams… will turn to nightmares!"

Disheartened, the Doctor turned, and ran.

Author's Notes:

Wait, did that just happen? No, I can't kill Charlie, I like him too much.

Perhaps we are already in a nightmare of the mind created by the Mara? Perhaps nothing has been real this whole time?

In case any of you are interested, I have uploaded several tracks to soundcloud to accompany the Twelfth Doctor Adventures, including 'To Temptation', to bring the adventures to life a little. (As Wanderer_In_Time, /user-651208930)