The Obligatory Disclaimer: Unfortunately, I don't own Doctor Who or any associated characters, creatures, features, gadgets, gizmos or TARDISes.
The Master barely had the energy to move from where he sat, back to the wall and huddled, shivering and burning from within. The drums seemed to be growing louder with every breath he managed to force into his lungs – or was it just that he could no longer find the energy to force the relentless beat to the back of his mind? Constantly, the gnawing hunger tore at him – he ate and ate, but no matter how much he consumed, the food could no longer sustain him and the energy simply dissipated itself through his translucent flesh.
The Doctor felt totally powerless – no, worse – useless. He would have done anything, everything, to save the Master, but he could do nothing, only help his former enemy to cling on to life for as long as possible.
"There's always the Chameleon Arch," he suggested from where he sat a few metres from the Master in the dim light of the medical bay.
"Oh, come on!" The Master's voice was a barely audible whisper. "I'd rather die a Time Lord than spend another day as one of those pathetic humans."
"You don't know them. I mean, really know them."
"I don't know how you get so attached to them." For a brief second, the Doctor broke eye contact, and the Master raised his eyebrows. "Ohh…something's happened, hasn't it? Let me guess – one of your pets? Yes…you lost another one, didn't you?"
"That's enough!" the Doctor snapped fiercely, and the two fell silent for a long while before the Master spoke again.
"It's always the women, eh?"
"What do you mean?"
"It was her fault again. Lucy – my 'faithful' Lucy – she sabotaged my resurrection."
"How?"
"She had a potion…said her family's connections had calculated the 'opposite' of the Potions of Life." His eyes were yellow orbs in his skull, but the Doctor detected in the tone of his faint voice that he would have been rolling them in disdain.
"Well it can't have been the opposite, or you wouldn't be here at all."
"I know that," the Master snorted. "Just some sort of toxin, it must have been. No – what I'm curious about, Doctor, is this: if you'd got there first, if the explosion at the prison hadn't been a fixed point…would you have stopped them bringing me back?"
The Doctor couldn't answer, not even to himself. He let the question hang in the air, pushing it away as his mind wandered, and eventually said
"'Dimensional instability', the TARDIS keeps trying to tell me. Little red light. Don't like little red lights – they're never good." To his surprise, the Master lifted his head with a start. His pale, gaunt face was visible for a moment and there was a dangerous glint in his eyes that made the Doctor involuntarily draw back.
"What? What is it?" he demanded. The Master closed his eyes and inhaled long and deep, as if savouring the air, and again the Doctor caught a glimpse of his face which wore a satisfied smile.
"You're not going to like it," he replied happily, his voice growing stronger by the minute. "You really ought to watch your back more, you know that?"
"What are you talking about?"
"Still can't see the obvious, can you?" the Master teased, and then had to bite his lip to stop himself from crying out in pain as the Doctor gripped his shoulders urgently.
"What have you done?"
"No – what have you done?" said the Master through gritted teeth. The Doctor met his eyes and, frustrated, suddenly pulled him to his feet, pinning him back against the wall by the shoulders before he collapsed. He laughed, and was suddenly behind the Doctor, standing unsupported in front of the large window that looked into the containment room of the medical bay. The containment room was darkened, the window an opaque rectangle; the Master raised his eyes to the ceiling and the lights flared, as if the switch had been flicked. In that instant, the window reflected the scene in the room – the Doctor, who had found himself with his hands pressed against the wall where moments ago the Master had stood; and the Master watching him, almost fidgeting with restless anticipation.
"It's been there long enough – you must have done something by now!"
The Doctor caught sight of his own face gazing back at him in the window, and his stunned expression slowly darkened to one of horror at the image that now became so terrifyingly clear – the massive, scarab-like insect that clung to his back.
"Oh look, Doctor – I think you might have picked up a bug!" said the Master, and he laughed again, the old manic excitement back in his voice. Frozen with shock, the Doctor could only stare, and the Master ran his fingers through his hair, tilted his head back and closed his eyes.
Silence.
An ecstatic giggle half-escaped his lips, and all of a sudden, in wild exultation, his whole body was fizzing with sparks of blue energy as he shrieked to the crackling air,
"IT'S GONE!"
Again, his face became visible, and the Doctor shuddered at the emptiness he saw behind the wide eyes lit with an insane fire.
"The drums…the noise, the constant noise…at last, it's gone!" He sounded almost hysterical now.
"But…why?"
"Because, Doctor," the Master replied breathlessly, "because that is my reality!" The Doctor had rarely felt this utterly overwhelmed, but every instinct he possessed was screaming at him, telling him that something was very, very wrong. His hands dropped to his sides and he slowly crossed the room to stand facing the window and his reflection which showed his face taut with anxiety. He scrutinized the image carefully, studying the figure of the Time Beetle that he carried. There was something different about this one – it wasn't quite like the one Donna had encountered. For one thing, it was shorter and squatter – a gravid female.
"These ones are feral," said the Master, watching the Doctor with an infuriating air of patience like a teacher trying to communicate a basic concept to a child. "Much more dangerous."
"It didn't bring me back in time," the Doctor muttered. "I'd know if it had…"
"Of course not – you're a Time Lord, idiot!" said the Master scornfully. "No – all it could do would be to hijack a decision you made after you picked it up and cause a split in your timeline, then feed off the potential energy from the parallel dimension it created."
"'Dimensional instability'…" the Doctor realized aloud, although that was only one part of the puzzle. And then his eyes widened as something occurred to him. "'These ones' – you mean there are more of them?"
"Ooh, you are on to it!" the Master grinned, and without warning, the room was plunged into blackness. The Doctor heard the Master's footsteps heading for the door, could see the tendrils of glimmering energy that ran across his body, illuminating him in the darkness. Heart pounding, he raced after him down the corridor, but the Master seemed to have regained that unnatural agility he had displayed on Earth, and with one gravity-defying leap, he was gone. By the time the Doctor reached the console room, the TARDIS was in flight and the Master was standing triumphantly behind the controls. He hurtled up the steps to the deck, reached the top step…and found himself starting from the bottom again, and again, and again, like a looping video clip.
"Come on, then! Aren't you going to try and stop me?" the Master taunted, leaning casually back against the railing a few feet from the Doctor, hands in his pockets. Carried perpetually forwards by his momentum, but repeatedly flung back to after the initial movement had started, the Doctor was unable to control his mad dash up the stairs and could only continue, over and over.
"How are you doing this?" he gasped. The Master sauntered back to the control panel and idly adjusted a dial before answering.
"Think of a fractal. A complicated one, if you like – doesn't look like you're moving anywhere any time soon."
"Where are we going?"
"Now, you've got that passenger there, causing a branch in your timeline and feeding off the energy. What if the decision you made that it hijacked was so big, so significant, that it created enough energy for the Time Beetle to continue its life cycle, sending its offspring in both branches to find another host. And then that host made a decision – another branch – and that Beetle's offspring spread and spread, and the timelines branched and branched. That's your fractal – that's a lot of parallel dimensions. There's only so many that reality can sustain, you know. Reality, Doctor – reality is disintegrating."
"But…how are you…controlling it?"
"Don't you think," said the Master, turning his head away, his voice now bitter and, the Doctor thought, tinged with sadness, "that after a lifetime of being told I was mad, I've had a good long time to think about what exactly reality is?" The recurring loop around the Doctor broke suddenly and, unprepared, he stumbled and fell hard on the deck.
"You don't know what you're doing," he protested. "This is dangerous – we should-"
"Ah, but that's where you're wrong, Doctor," the Master whispered, kneeling down to face the Doctor. "Because this really is my kind of world. And you know what?" He stood up and headed for the door. "There's a whole planet out there that's going to start falling apart at the seams very soon! And a whole population of primitive creatures that will need someone to restore a bit of order, make things how they expect them to be, so they can carry on with their mundane, realistic lives. They're going to need a Master!"