"So, you're the one behind all this"

The man stood on the outside of the Citadel, his hands thrust in the pockets of his brown overcoat, his brow furrowed as he stared at the anomaly in front of him. It's form was shifting. It seemed to be trying to take the shape of his greatest failure, someone he'd failed to save because it was Rose one second and Donna the next and when he looked at it the wrong way he swore he could see the sun reflecting off familiar silver leafed trees.

"I am The Catalyst"

It replied.

"So this was all a trap for them then? All this rubbish about the crucible, all that just to lead them here? Why?"

The man asked.

"It is to test their evolution, to serve as a warning gauge for their resistance. As each cycle has given way to the next it has left it's mark behind. Eventually, this lingering memory will become too great. When the organic species have the strength to resist the Solution with the Crucible, then it is time for it to be replaced-"

The man casually interrupted him.

"But that's the thing about humans, isn't it? They always surprise you. They're just a bunch of big, stupid uncivilized apes, aren't they? Wrong. They always crawl back. They grow, they change, they evolve. Live to the end of the universe that lot do. I should know, I was there. They changed the design. They hacked you."

The hologram continued, seemingly unperturbed.

"Organics have proven unpredictable. They are a variable which is difficult to account for."

"And that's the one thing you can't stand."

He took every opportunity the thing gave him, bouncing every misstep into his own speech.

"Anything that doesn't conform to your world view. Anything that falls out of your programming."

He took out a small silver device with a blue light in it and aimed it at the projection. It made a buzzing sound.

"Makes perfect sense, really. You're an AI, a good AI but not a great one. Cleverly programmed to solve a task by brute force, but no real foresight to your programming. That's probably why they didn't see it coming, no foresight. What was your reasoning for killing them? What twisted logic brought them to their knees?"

The projection seemed as taken aback as it could be for a moment. Then it struck a nerve. It's shape changed again, to a face he'd been around for all one of his lives but rarely seen. He knew it all the same. A thin faced man in a leather jacket, simple black t-shit and short hair.

"It was the only solution to the problem."

Said the impression of The Ninth Doctor.

"The only way to save the galaxy, to fulfill my purpose. I was created to end conflict between organics and synthetics. In every effort I made the synthetics invariably rose against the creators, and if the creators survived their children's onslaught they invariably made a new model which would take it's predecessor's place. The only way was to prevent their construction. The only way to do this was to end the constructors. I killed one race to ensure the future and survival of a thousand others. With one stroke I killed my people and ended the war."

All the whimsy had gone out of The Doctor at this . No more was he the healer or the wise man. The Catalyst had just unleashed the Oncoming Storm.

"And these are the choices you'd offer the puny organics now they've proved themselves worthy of your pity. First you offer them a way to lose their humanity. A way to make themselves perfect in your eyes. I've seen the way that ends. You wouldn't know Mondas, it fell too far out of sync in your...cycle. But I do. I've seen the horrors that planet brought, I've seen what the people who lived there did to themselves. I fought them. I ended them. I will not see them return by anyone's hand, least of all yours."

The Catalyst, realizing too late that letting The Doctor talk usually heralded imminent doom, decided to try to interrupt him.

"Synthesis is the final evolution of organic life, the last step on the road to perfection. Can you, even now, imagine your life without machines? Can you-"

The Doctor cut him off, his rage starting to show.

"That isn't the choice you're giving them. You're giving them the choice to lose everything they are in a cybernetic shell, not a choice to live with or without technology. That's obviously what you'd like them to pick, if organic life became synthetic life your long mission was finally over, wasn't it? No more separate organic and synthetic, no more conflict between them. It never occurred to you that the universe might like diversity, so you just decided to lump everything together and stop any possible cultural progress. But oh you knew they were too clever for that. You knew you couldn't strong arm them into one choice from the Crucible, you had to give them another option. Something you could handle but something that seemed like it gave them a choice.

So you took a gamble. You gave them the ability to upload one of their own into your data core to serve as the new Reaper intelligence. Well, that's what you'd make it look like. Somewhere, back in the deepest recesses of that hard drive, you'd always be waiting. Always watching, always guiding your successor down the path you followed if they didn't follow it themselves. Sure, you had to make it look convincing, you had to actually give them the power, you couldn't do anything unless they let you. But you knew they would. Eons, alone, at the head of the strongest fleet the galaxy has ever seen, watching organics fail constantly, having the power to step in whenever you liked, change everything however you'd like. That kind of power, that kind of loneliness, that kind of cynicism for that long, anyone would crack. Anyone would turn into a tyrant. They'd turn into you."

The catalyst switched forms again. An even lower blow this time. A man in black, with a very big hat and murderous contempt in his voice. A man The Doctor had met only briefly but would spend the end of his life with. A man who haunted him more than anything else

"And what, Doctor, have you done in your eons of solitude?"

The Valeyard asked.

"On the run from your own past and your own future. With the power to have planets live or die, to end any conflict as you so desired, gallivanting about the universe in the last TARDIS, writing a name for yourself in blood on the stars. What have you become in that time Doctor if not a tyrant? If not that which you most hate?"

The Doctor smiled. A dark, mocking smile but with a hint of genuine amusement and victory to it.

"You're not looking in the right part of my memory. I doubt anything as rudimentary as you could process the whole thing at once, so I'm going to show you myself. Brace yourself, this is going to hurt."

And he threw his full psychic power at The Catalyst. He showed it what it hadn't seen, what it had dismissed as irrelevant. Every companion. Every time one of them left, every time one of them died, every time one of them had held him back. And most importantly, what had happened just a bit before he came here. Adelaide Brooke. What had happened when he hadn't had anyone left to hold him back, when he'd become the Time Lord Victorious.

"That's what I did with my eons. I found people to share them with. People to hold me back. Ways to stop me turning into you. I don't deny I've done things I'm ashamed of. I've ended worlds. I didn't take lives, I manipulated people into taking their own. But I came back. I became The Doctor again. The man who makes people better. Funny, I always needed people to stop me from becoming worse. Just didn't always know it."

And he brightened again, happy to be off his own inner darkness.

"But back to your plan. Had a great, big, gaping, human sized hole in it, didn't it? A hole called the Crucible. They changed it. They got their hands on the design, they built it and they improved it. You based those designs on your creators' tech. You missed something. It had a safeguard. A self destruct mechanism. The organics found it, freed it, built it back in. Didn't know what they were doing of course, that's the best part about humans. They usually hit the mark when they're firing blind. You couldn't turn it off. It was designed for you to not be able to turn it off. But you could give it side effects. Something that seemed to go along with it as a choice. Something horrible. You didn't think anyone would pick genocide over a cyborg utopia or ultimate power, did you? Nice little trap you'd built yourself. Your atrocity of a utopia, a new leader to corrupt to your will, genocide or letting the cycle continue. Didn't leave them an option they could stomach."

He turned serious again.

"You've read my mind you know my reputation. Earth is under my protection. I'm not letting you get away with it. No one thinks of everything and there's always a way out. You get one chance. Just one. Walk away now. Call off your dogs and retreat back to dark space, maybe come back when you have something to offer society. Live out your life without massacring billions of innocents. I'm giving you a way out. I suggest you take it."

The Catalyst shifted again. Into a form it knew would jar him at a moment like this. Flowing orange robes, dark hair, an iron glove and a scepter, Rassilon was unmistakable.

"It seems to me Doctor that you are the one in need of a way out. Your choice may be more elaborate than the last time you made it, but it remains the same. Condemn billions to die or watch billions of others die in war. I am curious to see which path you choose this time. Will you end a newly blossoming species to end me? Will you believe yourself to be able to endure the eons without interfering? Will you see the sense in my utopia? Or will you simply do nothing, watching as innocent blood is spilled? A curious choice Doctor but not one you're unfamiliar with."

The Doctor smiled faintly. The smile of a victory he wished he didn't have to win.

"That's a choice I hope I'll never have to make again. And definitely not today. First thing I thought when I heard the control option -Well, second thing, after the tyranny and the corruption bit- Was that no one would ever entrust that to transmission. The most important upload in hundreds of thousands of cycles. The one moment it all came down to. You'd want a hard connection. Can't risk a jarring hit to the station at the wrong time knocking out the wi-fi. Which means that device is linked straight into your data core. The data core that controls and coordinates the reapers. Which means that I can do this!"

He pointed the screwdriver at the control device and a high pitched whine echoed across the citadel.

The reapers outside stopped moving. They stopped flying. Those that continued crashed into each other. Some started firing their weapons randomly, hitting their fellow behemoths as well as the allied fleet. And it was at that moment that the remaining organic forces realized that even a god can die.

On the Citadel the Catalyst was shriveling, dying, shifting forms almost faster than they could be processed by the human eye. But The Doctor saw each and every one in it's death throes, crying out for mercy.

"I'm sorry. I'm so, so sorry."