"No!" The Doctor shouts.
The Mistress steels herself to not turn back to him. Not now. She couldn't. She doesn't remember much but she remembers enough that she has carried around a dematerialisation circuit for hundreds of years and enough to know that when she was him she killed the woman who gave him that advice.
She doesn't want to die but it has to happen- has already happened- and for that she must leave the Doctor, let him believe that she has turned away from his ideals again.
It is fitting, she supposes as she keeps walking away from the Doctor's protests.
She will die for him. Without hope. Without witness. Without reward.
He will go on believing she lived, betraying him.
She will die chasing her own tail.
He stands in front of them.
"I'm going to be dead in a few hours so before I go let's have this out. You and me. Once and for all." He says more quietly. The Mistress looks away, wants to tell him she will too, can't because she knows he would try to stop it.
He huffs, turning away from them both momentarily.
"Winning. Is that what you think it's about?" He asks them. For the Mistress there's only one thing left to think about. The one thing she can't say.
"I'm not trying to win. I'm not doing this because I wanna beat someone- because I hate someone or because- because I wanna blame someone." He exclaims, looking between them. Missy can't look at him, knows his speech will fall on deaf ears and soon-to-be-dead ears.
"Not because it's fun." He says, "God knows it's not because it's easy. It's not even because it works because it hardly ever does!" The Doctor continues, gaze still switching between the two of them.
"I do what I do because it's right!" He shouts, staring at the Master. He doesn't care and the Mistress wishes that she couldn't care- just a moment would be enough that her hearts wouldn't tear themselves to pieces. Just a second's reprieve from the pain in her chest which she knows will only get worse.
"Because it's decent!" The Doctor yells, "And above all it's kind." He says, voice dropping as he looks back at the Master.
"Just that!" He says, looking at the Mistress. She looks at him briefly, shoulders tense and tries to offer a smile- just that sign to let him know that she is listening and only wishes she could stand with him. It falls flat on her face, not even making more than a small twitch of her lips. He seems to see the shift regardless and looks back to her previous incarnation.
"Just kind." He says, a broken man.
"If I run away today... Good people will die. If I stand and fight, some of them might live- maybe not many- maybe not for long." He turns back to the Master, "Hey. You know, maybe there's no point in any of this at all but it's the best I can do." The Doctor pauses and Missy blinks back tears.
"So I'm gonna do it. And I will stand here doing it if it kills me." He ascertains.
"And you're going to die too." He says, pointing at the Master. He turns to the Mistress, more hesitant now. His finger lowers and she still can't bring herself to look at him- knows how much it will kill him when he eventually finds out.
"Someday." He says, softer somehow.
Today. She wants to correct him
"How will that be? Have you thought about it?" He asks the Master this time, "What would you die for?" He asks. The answer burns in the Mistress' mind.
You. She holds behind her shields. Always you. I kill him for you. He dies for you. He kills me for it. I die for you too.
"Who I am is where I stand. Where I stand... Is where I fall." His voice breaks and the Mistress knows that she has never been closer to the Doctor than now.
There is a pause and he steps forwards, towards the Master.
"Stand with me." The Doctor requests and the Mistress wants nothing more than to do that.
"These people are terrified. Maybe we can help a little. Why not, just at the end, just be kind?" He asks him. He won't be. She knows that. He is not kind. He won't be kind for a long time- until he is her.
The Mistress still can't look at the Doctor, watches the fake grass around his feet. She tries not to listen as her past self breaks the Doctor's hearts- knows that she will be breaking him soon.
The Master leaves and the Doctor watches him go, makes to follow him.
He notices she hasn't moved yet. She only wants to stay with him a moment longer- just enough to hold her until she dies- that's all she wants.
"Missy." He says softly, almost disbelieving, "Missy." He repeats and she wants to fall into his arms and tell him everything. She settles for looking at him, memorising his face and holding back her tears. He sniffs.
"You've changed." The Doctor states.
She tries to deny it- knows that she will cause him pain in just a few moments.
"I know you have." He confirms, "And I know what you are capable of." Tears glisten in her eyes.
"Stand with me." The Time Lord asks, "It's all I've ever wanted." She smiles a little, crying now. It's all she's ever wanted too. Why can't he see that- why does he have to make this harder for her?
"Me too." She admits finally. Just before she dies she can give him this much.
The Doctor reaches out for her- his hand wrapped in bandages. She looks at it and wants to take it- catalogue the feeling of his hand in hers, dissect it down to the barest elements and memorise every detail. She thinks she might deserve it before she dies- just this moment. Could she?
"But no. Sorry. Just... No." The Mistress says, trying to act like her denial doesn't make her feel like she's already dying. She goes to walk past him and he grabs her hand, bringing her close to him.
"But thanks for trying." She says.
She means it.
She squeezes his hand, giving him some of her strength and taking the feeling of his hand in hers with her.
The Mistress forces herself to let go.
Before he can try to stop her again she passes him.
She knows if he did ask again the temptation would be too much.