At the end of it all, after Gallifrey, what would the Master have done with the Doctor had Ko Sharmus not arrived?
Option one: killed the Doctor. Yawn, boring, not the Master's style.
Option two: made the Doctor join him in his destruction.
Now, option two also has two options. Both start very similarly though: the Master makes some grand speech, to 'recruit' her to his side. He convinces her that he's in the right, and she joins him.
Now here, option one is that this works on the Doctor. She joins him, she becomes evil, she revels in the destruction. Maybe it happens slowly, he starts her off with the Daleks and other evil empires that she can agree to destroy, and before she notices half the universe is gone, and she's loving the hell they rain down. Classic dark Doctor.
But here, option two is that she's a liar. And she is, really. Here, she joins him, as she did in option one, though perhaps more reservedly. The Master notices, but is fine with it: fine, he thinks, I'll break her down soon enough. But hey, the Doctor is a liar, and the Doctor is thinking the same thing.
As in option one, he starts her off with destroying some Daleks. It's easy, he says, you can do it, he says, you've done it before, he says. She does, in the end, but not without dragging him into an argument about morals. He wins, but she can see the doubt in his eyes. One point to the Doctor.
She only destroyed the Daleks because a child happened to wander onto the battlefield anyway.
The pattern continues. He points her to bad, she points him to good. Mostly it’s a stalemate, sometimes there's a winner. He backs down sometimes and gets the job done himself, and occasionally she'll see the benefit of destruction. They find middle ground surprisingly often. Maybe she'll suggest a new plan that saves everyone, or save the day by making a big speech, and he'll join because a child smiled at him. Maybe he'll destroy someone because they were trying to destroy someone else (her, probably, knowing him), and she won't quite be able to find it in herself to disagree. Stalemates.
Of course, it all has to come to a head eventually. They might be having a quiet day, or perhaps have just come back from a stalemate, when the Master finds the Doctor. In the library, most likely. Libraries are great.
"Hey!" He'll say, "I know what you're doing!" He's shouting, and probably pointing, dramatic little dear.
"What?" She'll say, maybe not even looking up from her book, "reading?"
Then he'll sigh, of course. "You're turning me good."
This time, she will look up. "Really? You don't look much different." She'll squint, and then grin that cocky little thing that always makes him want to punch her.
"You know what I mean," he'll say, but what he will really mean is 'fuck you and your stupid mouth'. "I barely even considered bombing those people today."
"And I nearly didn't even come up with a plan to save them," she'll respond, mouth thinning temporarily. "I'm not the only one doing the turning" and then her eyebrows will raise.
He'll step forward, hands curling into fists. "So what? We're turning into each other?"
Then maybe she'll stand- no, rise, she'll rise- and smile at him. It won't quite be kind, but it will bring him something new to feel. "Maybe. Would that be so bad?"
"Yes," he'll spit, and rage, but only until she interrupts with:
"Well then. Let's see who breaks first."
Then they'll stand there, staring at each other, neither actually willing to move. Who breaks first will become a metaphor, and they are already both too close to breaking. Eventually, she'll move, maybe by flopping back into the chair or turning away or by backing away slowly- yes that's it, she'll back away slowly, avoiding the chair with uncharacteristic grace- and the spell will begin to break. One of them will wink, though maybe not both (but if she winks first he'll wink back when she can't see). It probably won't take him long to leave the library, but she'll stay. She'll have her book to finish, of course.
After all that, they won't have long. Once the tension has built for them, there's no stopping it. The pressure will rise, and the storm will come.
There'll be things before that though. A couple stalemates, a couple wins for her, a few triumphs for him. She'll build him up gradually, at first encouraging him just to save a child, then two, then their parents, then their whole families. He'll be gradual too: first just get her to kill the evil monarch, then their enabling family, then their whole corrupt government. You're doing it for one, may as well for all.
Three months, let's say. They'll probably get three months out of that, then they'll need to have a conversation. By then, he'd be more conflicted than Missy, and she'd be close to changing her name. After all, Doctors don't do the things she has done, and Missy did come so close.
She'll take them to the place they have their conversation. By then, it will be clear to both of them that they're not going to kill the other, and he had never had a reason to lock her out of the controls anyway. So he'll let her say, one day, out of the blue but not really "we're going somewhere together," and he'll simply watch as she pilots his Tardis. By then, they'll probably call it theirs, but she'll sometimes feel sentimental for her old blue box, so he'll have to respect that.
She'll take them to a little forest clearing. Maybe, maybe the grass will be red, but she won't have meant that. He'll just be grateful- at this point, he'll break out in hives if he ends up on earth- so he'll sit, on a helpful log, and wait. If the grass is red, she'll hesitate, but she'll end up joining him, just as she will if the grass is black or yellow or sky-blue pink. If it's green, he might not sit at all.
They'll probably be feeling awkward by then- it's hard to be comfortably dramatic when sat on a log- which means they'll talk together.
"So," they'll both say. There might even be a pause for them to laugh, a pause which will be filled in every scenario that the grass isn't red. Where it is, they'll just stare. Here, the grass is probably not red. It's a rare colour for grass, thankfully.
After the pause, where they probably laughed, he'll let her start. She'll be the one with most to say, after bringing them here.
"I dunno how to word this," she'll say, simple like her humans, who she won't have seen for months. "Do you?"
He'll shake his head. How would he know, when this conversation would drive his past selves to self-destruction?
"I'll just wing it then," she'll sigh, and he might as well smile. Silently, obviously.
"So, um. We've been doing this for a while now, and I think… you know… I just mean that," and here she'll pause, aiming for him to continue. He won't though- how can he find the words without her? He'll nod instead, and provide a near replica of encouragement with a smile. He'll probably refuse to meet her eyes too, show a little vulnerability.
Now she'll sigh, having gotten no help in wording. She might smile- but then, no, likely not, it's not quite the right time. "I mean- it's been good. We've been good. Both of us, we're better now."
He'll want to laugh, and deride her use of the word good. He won't. Instead, he'll be buoyed by her use of the word both, and will reward her for the admittance.
"I've certainly enjoyed hearing less of your morality speeches." Maybe she'll like that, and will smile. Her nose might even scrunch at the tip, and wouldn't that be a reward. He'd seen it once as O, and once would never be enough.
"Exactly!" She'll say then, "and I've learned stuff from you, too-"
And then he'll interrupt- "there are definitely less Daleks floating about in the galaxy." He'll tilt his head up to the sky. Will there be stars? No, no, they need daylight, to see each other, so the sky will be bright, green or indigo or yellow. It'll make her laugh again, despite their nerves. He could look back at her- actually, he will, just to see the smile he caused.
She'll gaze at him, then keep talking, because that's just who she is. "Yeah. So, I think we should, erm, we should stop changing each other and just- travel. Together."
He'll look at her, and see the deep fear that she'll carry, and the deeper hope. He'll remember all the easy times they've had over the past months: the giggles in the console room, the friendly jibes as they run, the foods they've bonded over hating. Images of her will play in his mind, and he'll have only one answer.
That's when she'll smile, nearly breaking her mouth open with the sheer brilliance. He's- no, they've- they've won.
Then what? Will they kiss? Oh, god no, they're not children wine drunk for the first (third, seventh, twelfth, fourteenth, fifteenth, eighteenth, twentieth, twenty first, thirtieth) time. They wouldn't kiss. Smile at each other again, certainly. Maybe they- oh, they could hold hands! Yes. He'll put his down first, in the tiny space they've left between them. She'll notice immediately, but the reaction will take a second. Cautiously, ever so slowly, she'll look at his hand. Then she'll put hers over it, in a much more assured fashion. She might even squeeze. They'll definitely smile at each other then, taking each other's breath away. Then the, then the sun could set. Yes, and then they'd watch the stars come out together. That's when they'd choose the first to visit, and they wouldn't let go of each other for a long time.
Yes, the Master thinks, that sounds nice. Holding hands, and a future with the Doctor. That's what he wants.
He thinks of the feel of the Doctor's hand, and smiles. He sighs when the smile breaks open his split lip again. The sigh brushes his burnt shirt over his worse-burnt chest and wrings another wince out of him. He's really not long for this world.
The death particle nearly got him. It wouldn't have, except the Cyberium expected it to, and tore itself out of him. He's little more than a lattice of injuries now, and it's impossible to tell what was actually caused by the Doctor's meddling human. His only solace is that the Cyberium is on its way out too, burnt by the death particle for being too alive. Sucker. He's glad to outlive it.
He's less glad to have to outlive his cyber Masters. He'd liked them. Even the Doctor had. Not the real one, his fake but happy dream one. They'd bonded over making them better, making them right. In his little daydream, she'd even used them against some people occasionally. They'd done exceptionally against the Daleks. He's pretty sure he could get the real Doctor to like them as well.
Oof, there's another death twinge. He'll start glowing soon. Time for another idea, then. A nice soft one, to end his life right. If they- the being that is the Master- are lucky, maybe it'll even start the next one right. It might even inspire them to do what their predecessors couldn't, and make it work with the Doctor. Now that’s a disarmingly pleasant thought.
So, they'll travel together. Every star, that's what they'll see. But where to start? Somewhere he hasn't been yet, let the Doctor play tourist guide for once. Metebelis three! The Doctor took that Smith woman there, once, and Miss Grant. It's high time they went together. He'll hold her hand, to let her guide him through, and tease her about her eighth body's fear of spiders. He'll keep his laser- built with her approval, of course- brandished, just in case any of those things dare to come near her. They'll see the shiny crystals together, and they'll smile harder than either are used to, and they will laugh about days gone by, and
And so the Master- this one, for there will always be more- slowly dreams himself to sleep.