There are patterns in the Doctor's lives
Disclaimer: Characters and situations owned by the BBC.
Spoilers: until The Doctor's Daughter, with some foreshadowing for The Stolen Earth.
Author's note: meta disguised as fanfiction, in a way, and while it uses Old Who canon as well as New Who, I hope it's accessible to New Whovians who haven't watched a single Old School episode.
The Doctor is in his third body, and just starting to adjust, badly, to a linear life, stuck at one point in time. He's working with UNIT - for UNIT, if truth be told, though he tells himself he's doing the humans a favour, he's not really their subordinate, he's helping, that's all – because if he has to stand still, they at least allow him to channel his energies into something useful. Something resembling his old life as much as it's possible while being in a very generous prison, courtesy of his own people. Besides, he likes the Brigadier, whom he has met and worked with before. His own impatience with the military notwithstanding, he respects the man. He trusts him.
Then the Silurians appear. Another sentient species native to Earth, much older than humanity, in hibernation through millennia and anything but thrilled to discover their planet has been usurped by apes. The Doctor tries to negotiate, tries to reach a compromise between the species, but the one Silurian who listens to him and is willing to reconsider is assassinated. The Silurians launch a first strike, a biological weapon, turning human bodies against them. The Doctor manages to trick them back into hibernation. He's young still, confident, optimistic. He'll wake them up one by one, spend time with them, convince them, and this time it will go better. More death will be avoided.
Except it isn't, because the Brigadier seals their caves and blows them up. When the Doctor sees the explosion and realises what it means, the mixture of shock, horror, a sense of betrayal and above all anger chokes him for a moment. When he can speak again, there is no doubt in his mind.
"That was murder."
The Doctor is in his tenth body, barely, just starting to adjust to it, the regeneration not yet settled. He is quite old now, new physical appearance notwithstanding, but he feels like he's been granted a new lease on life. He's surrounded by Rose and her family, and Harriet Jones, Prime Minister. Brilliant woman. Innate distrust of politicians aside, he's met and worked with Harriet Jones before. He respects her, he trusts her.
The attempted invasion by the Sycorax was a close call. But that's settled now. Predictable people, the Sycorax, with their warrior creed, but not as one track minded as the Sontarans, luckily, and not nearly as technologically advanced. Being able to regrow his hand because he's still within the first fifteen hours of his regeneration cyle was a bonus – he doesn't really fancy spending a lifetime one-handed – but even if that hadn't been the case, it would have been worth it. One hand, that's nothing if you manage to avoid a war between species.
Then Harriet Jones orders Torchwood, whoever they are, to fire at will, and the retreating Sycorax ship is blown out of the sky. Rose gasps, Jackie puts her hand on her mouth, but the Doctor doesn't really notice either of them. His attention is focused on Harriet Jones, and the mixture of anger and betrayal he feels is all too familiar. When he can speak again, there is no doubt in his mind.
"That was murder."
For a good while after the Silurians have been wiped out, the Doctor doesn't talk to the Brigadier. Liz is running interference between them, and when the Brigadier does ask for his help again, the Doctor can't refrain from asking whether the Brigadier has murdered any aliens lately.
He can tell from the expression in Liz' face that she thinks he's being unfair. Of course she does. The Silurians threatened her species; she might not have approved of the Brigadier's methods, but she's glad of the result. Better she thinks that he's unfair, though, than realising the truth, which is that he's a coward. The death of the Silurians sickened him, but he can't bring himself to draw consequences that really matter. He doesn't leave UNIT, or turn against the Brigadier in any way other than through ineffective words. Not because he can't, but because doing so would mean giving up what makes his exile bearable. The laboratory, the access to what mysteries this planet in this time zone has to offer, the company. He has never done well on his own, and in this state, with part of his mind clouded and his TARDIS just as broken, the idea of living on his own frightens him. He's dependent, and the sense of powerlessness, the anger with himself for being so is something he'll never forget.
"Defence," she says. Of course she does.
"They were leaving," the Doctor protests, but he can see on Harriet's face it doesn't matter to her. She thinks she just prevented the Sycorax from coming back, saved her species through a pre-emptive strike, just as the Brigadier did all those years ago with the Silurians. The Silurians, who as it turned out were not completely wiped out. Some of them had adapted for a life under the sea, and they were even less inclined to believe that peace with the human race was possible once they found out what happened to their brethren. But the truth, the truth which the Doctor will only admit to himself, is that the thought Harriet's actions could provoke the remaining Sycorax to send another ship isn't the main reason for what he feels right now.
He's not young anymore, and he doesn't have the excuse of a clouded mind and an exile for not drawing consequences. He doesn't even have the excuse of naiveté for not paying attention and not predicting what she would do. "I should have stopped you," he says, and now she is angry as well.
"What does that make you, Doctor? Another alien threat?"
She's right. He's not human. He can see time unfolding around her, what was, what is, what could be, what must not be. He is not human, and in a moment fuelled by past and present alike, he does what his people were never supposed to, what caused his exile so many years ago in the first place. He interferes. Out of the myriad of possibilities the life of Harriet Jones offers, he chooses one by speaking six words.
The next encounter between humans and aliens, the Probe 7 affair, ends better, with the Doctor able to negotiate peace between them. He doesn't apologize to the Brigadier, and the Brigadier doesn't apologize to him, but there is an awareness they've made their own peace with each other, despite still convinced the other was wrong. They never mention the Silurians again, not until the Master is captured by UNIT, and there are quite a few voices calling for his execution. He's responsible for at least as many dead humans as the Silurians were, and he doesn't have their cause. He's also not an entire species. He is one man.
"Geneva is asking for my opinion", the Brigadier tells the Doctor. "He already nearly caused World War III once, and nobody has forgotten that. Can you seriously tell me he'll ever stop being a threat?"
The Doctor can't, and while he's not above lying to his friends on occasion, it doesn't even occur to him to do so this time. He's too aware that the Brigadier is offering to do now what he didn't with the Silurians: trust in his judgment. This deserves nothing less than complete honesty in return. He has already made his own suggestion regarding the Master: imprisonment. Which, truth to tell, would have benefits for no one but the Master, who might be kept from harming others for a while but more importantly won't run out of regenerations while disbelieving humans execute him again and again.
"If I weren't here anymore," he says, not really looking at the Brigadier, because it isn't easy to spell this matter out to oneself, let alone to someone else, "then I don't think he'd bother with Earth, either."
"I see," the Brigadier says, with a neutral expression that gives nothing away. There is something to be said for this period's reticence among male conversations. The Doctor remembers visiting Earth 20 years later, when humans seem to be obsessed with discussing their feelings, and suppresses a shudder. "Well," the Brigadier continues, "that does limit the options. Since I'm not about to lose my scientific advisor. Even if you get that box of yours going again." He looks at the Doctor, and his gaze is shrewd and unrelenting. The Doctor is reminded of the fact the Brigadier, as opposed to Liz Shaw, had been entirely prepared for his little ruse back when the Time Lords first dumped him on Earth, had expected him to follow his first instinct and run.
"I'm going to recommend imprisonment to Geneva. Since we can count on you to be there whenever we need you, no matter how conditions may change for you."
It's a bargain being offered, plain and simple. Before his exile, visiting the Earth had been purely voluntary on the Doctor's part, and entirely up to the whims of the TARDIS and himself. He liked humans and liked helping them when chance would have it, but he didn't feel obliged to do so, or to check on a regular basis whether or not they needed it. What the Brigadier wants now is a promise in exchange for the Master's life, a promise that will extend beyond this body, this lifetime. The Doctor hasn't made vows to anyone since early in his first body, and he hasn't stopped running since then, either, not unless forced to. His own people certainly don't trust him to keep to their rules without force; it would never have occurred to them to ask for a promise.
"You can," the Doctor says, returning the Brigadier's look as directly, and though he has just shackled himself to this planet for the rest of eternity, he can't find an ounce of regret.
The Master rules Earth exactly one year, in human terms. During that year, time is a paradox, its natural flow warped, its countless possibilities twisted. Sometimes, when not weaving the threads of the Archangel Network together in his mind, the Doctor tries to follow the current line back to where it started to go wrong. Malcassario is an obvious and important point, but the intricate pattern that is now turned inside out offers other crucial departures that allowed for the current situation to happen. Tracking down one particular avenue, the Doctor finds himself and Harriet Jones, that Christmas Day. He's not the only one who does.
"I could see it when I met her," the Master tells him, in one of those fruitless conversations they have that start with taunts and end in silence, and that still happen because neither of them can do without them. "Here I was, rising hope of Britain meeting the Prime Minister in her decline, ready to be bored out of my mind because really, no challenge no fun, and then you made my day. It practically glowed around her, that timeline turned sideways. Such a lovely spectacle to watch."
If those six words had not been spoken and Harriet had been at her full strength, carried by popularity, the people of Britain might have not been swayed by the Archangel Network. More likely than not the Master would have had her assassinated, blamed someone else and would have risen to power in the wake of national grief and paranoia, but this is beside the point. The Doctor has never believed in excusing one's own actions by claiming someone else would have done something worse.
He does believe in doing something with the consequences of one's actions, his own as much as anyone else's. His body, aged up and down a few times now at the Master's convenience, is still his own, and it would be quite easy to find a way to permanently die. The power of words works in many ways; he could provoke several of the Toclafane, for example, whose glee in violence is aroused so quickly. It's doubtful that he would regenerate in his current condition, and he believes, now more than ever, what he told the Brigadier all those years ago: the Master would not bother with Earth if the Doctor as his audience weren't available anymore.
But if he dies now, there is no guarantee the paradox will ever be reversed, and that means all those millions who died since it started remain dead. If he dies now, and the Master leaves Earth without destroying it entirely in a giant fit of pique, it will take humanity centuries to recover, and they won't get centuries, not with the Silurians and their last attempt to take their planet back due in 2084, events that are fixed, and he already participated in. If he dies now, then his promise to the Brigadier will be broken, and this is the one vow, the only vow, he has always been able to honour.
He thinks of the last of the Silurians, currently sleeping under the sea, and his inability to find a way to save both them and the humans. He thinks about the Sycorax and Harriet Jones, and choices made, his and hers. He's young again, in a body forced on him, watching an explosion and tasting death and failure in the very air he breathes. He's old and reborn, and the ash of a ship full of living creatures reigning down on his face resembles nothing as much as snow while his life comes full circle.
In his mind, thousands of voices murmur, all different sounds. None of them are his own species; he has shut his mind against the only other voice of his own species still in existence because he has to, because the Master can't be allowed to find out what he plans. But it will all change. The end will be different, this time. He'll manage to save both humanity and the Master. There will be no burning bodies at the end of this road.
Once you have entered someone's timeline at a certain point and found out you did not see this person before that point, it's impossible to change this without risking destabilizing the universe, which is why the Doctor, having received Reinette's last letter, cannot go back and change her past so she would never need to write it. This is why he makes a point of avoiding encountering the Brigadier in the early 21st century and keeps returning to earlier points, before the millennium changes. The Brigadier is human, he will die, of old age, he has to, but as long as the Doctor isn't there to witness his death or learn about it shortly after, the Brigadier's personal timeline is flexible enough to allow for any number of earlier visits.
He breaks with this rule after the Sontaran incident, after bringing Martha back home. After Jenny. Colonel Mace said the Brigadier was in Peru, so the Doctor tracks him down there while Donna catches up with her grandfather. The Brigadier's hair is completely white now, and there are only a few possibilities in the time unfolding around him left, but his gaze is sharp as ever. It doesn't take him long to figure out there has to be a reason why a version of the Doctor seeks him out at this time, and not earlier, and being the Brigadier, he asks, point blank.
"Because," the Doctor says, "I need to ask you something, and the younger you wouldn't know who Harriet Jones is. Or what happened in these last years."
"I see," the Brigadier replies, eloquent as ever with those two syllables. The Doctor, uncertain the Brigadier in his semi-retirement would have been familiar with all the details, briefly summarizes what happened that Christmas Day more than two years ago. At least, "briefly" was the intention; as usual, words run away with him, until the Brigadier stops him by declaring "For God's sake, Doctor, you're giving me a headache."
"Are you asking me which of you was right, is that it?"
The Doctor shakes his head. "I know you'd agree with her," he says. "I knew that while it happened. That's why I want to know is what you would have done next, in her place."
"Drawn the consequences and tried again, I suppose," the Brigadier says, sounding somewhat surprised the Doctor needs to ask. "And made a tactical reassessment. You can be absolutely infuriating, Doctor, but there is no one I'd rather have at my side. Frankly, if one single electoral defeat were enough to send Harriet Jones into retirement, she'd never been able to give us a golden age to begin with. I never met the woman myself, but I did vote for her, and I'm sure she is not sitting around idly right now but busy doing her best to ensure the safety of the planet somehow. Given that you are our most efficient ally, your paths are bound to cross again."
He's both far younger and older than the Doctor will ever be, this human who knows him, all of him, better than anyone still alive. The Doctor concentrates and focuses, but while he can sense the planet itself moving around the sun, teeming with myriads of possibilities, he's unable to tell whether the Brigadier's prediction is among them. He hopes so. He has no idea what he will say to Harriet Jones if they should meet again, but for now the possibility is enough.
The Doctor sits next to his friend while the shadows grow longer, thinks about people saved and people lost, the last of them a girl who never even once felt the sun on her face and died because she listened to him and chose not to kill. He thinks about cycles, and patterns and the vain attempts to break them. And he knows that whatever will come, he'll try to break them again. This is who he is, in every regeneration.
This is the debt he owes.