So I actually quite like this as an ongoing story idea (which would probably end up shipping Bill and Missy in this new timeline- not going to lie). Say if you want me to because I don't promise regular updates but I can promise I'll work on it.
The Mistress runs her fingers across the keys, breathing in again the stagnant air. It moves in and out like she wishes she could of her cell. She's been here for a long time now- not quite the one thousand years but close enough. The Doctor had been exceptionally kind for these years.
She supposed.
After all he could have just killed her or left her alone in here without anything to entertain herself.
In return she plays for him sometimes. More she plays for herself and picks music she knows he likes if she can sense him beyond those doors. He brings her food sometimes. When he remembers so when he is hungry which suits her just fine because they seem to be strangely synced after all these years almost cohabiting.
She likes it best when he brings her stories though. Stories about dying are the best because in her better moments it's hilarious to hear about how some apes almost died and in her worse moments she can imagine that she is the one who is being killed.
He always has been good at telling stories.
She presses one finger down, letting the note ring out in her glass box.
Something in time shifts. She feels the shudder go through her as millions of tiny little things change. Her head hits the keys but she doesn't hear the song it plays.
"So you're just going to keep me?" Echoes around in her mind. Her first question to him. The answer swims from 'I swore an oath to protect you' to a simple 'yes'.
Ah- so her Doctor- something's happening to him. She manages to hold the original answer in her mind, grasps tightly to it as she feels everything since then attempt to crumble and reform.
When her memories stop trying to overwrite each other her head aches, processing two different timelines at the same time.
She forces herself to remain conscious- just enough to sort through everything. All she knows is that her Doctor is in danger, she can't lose herself now and risk forgetting…
After five hours, twenty-nine minutes and forty-one seconds the Mistress lifts her head.
The keys are imprinted along her face and she has shifted the new memories aside, firmly insisting on the old ones.
She hears footsteps at the door. The familiar weight of the Doctor's feet hasn't changed but there's a lighter step beside it. Judging by the gaps between steps and how many steps are taken against the Doctor's own stride she would say that it's a new companion, definitely human, most likely female.
Something from her old memories twinges and she gasps in pain, fighting against her body's instincts to stand and face the door in this timeline.
She will not stand for him. She is the Mistress and she will win.
The Doctor does not call out before he opens the door. Referencing her new set of memories says that this has been the case for several hundred years. She frowns, elbows lightly coming to rest against the keys so as not to bring out any sound. She taps her fingers together, flicking through a few more scenes to get a better idea of this Doctor.
Her heartbeats pick up as the door opens and she ignores this response, squashing down on- is that fear ? Almost but not quite. Apprehension? Nervousness? Something like that. This timeline has invoked in her a slight compulsion to worry at the Doctor's arrival. She digs a little deeper, rummaging through millions of moments to find the root of the emotion.
"Missy." The way he says her name bombards her with all the things she'd been searching for. The Mistress manages to hold back a cry as she lets her face go blank.
He is displeased. She knows him well enough to know that tone of voice.
She turns around at once, letting herself fall into the memories to at least get her through this moment. Elegantly she plucks up her skirt, curtsying low, head bowed. She forgoes the theatrics.
"Doctor." She murmurs, voice low. She waits in that position until she senses the incline of his head. Then she stands, eyes finding his directly opposite her on the other side of the glass. She does not blink or look away.
Rasillon how much she wants him right now- the old her- the one that isn't from this new timeline.
He nods, going to the only seat in the room and sitting down. She can see his companion is uncomfortable with the whole situation and dips into her mind.
Ah. She remembers. In fact she's the one who caused this whole mess. The Mistress is irked, thankful and ever so slightly flattered by the human.
Annoyed that she messed up history so badly and was currently giving the Time Lady a huge headache. Irritated that the human had been able to accidentally corrupt the Doctor more than all of her painstaking attempts to do the same. Grateful that she had because the thoughts it is filling the Mistress' head with are all incredibly... entertaining.
And then flattered by the huge flashing 'Oh-my-god-she-is-so-attractive-she-could-kill-me-right-now-fuck-why-is-she-so-hot?' short circuiting the human's mind. Only slightly though. The human is still only a human.
The human- she thinks the Doctor had called her Bill at some point- follows hesitantly, coming to stand at the Doctor's left.
"So you just keep your best friend in a display case?" Questions the human with a touch of outrage the Mistress appreciates.
The Doctor either doesn't hear it or doesn't care.
"Play." He commands, eyes fixed on the Time Lady.
The Mistress gasps a little, a ghost of a smirk making its way to her lips as she sinks to the piano stool, thighs pressed tightly together. Of course she disguises it as anxiety, even adding a bite of the lip as she flicks her gaze over her shoulder.
She begins to play his favourite song, automatically finding the keys beneath her fingers.
"She's evil." He says after a few moments to his companion, "Aren't you Missy?" He says louder, as if she couldn't hear him perfectly.
The Mistress turns, still playing, fixing her eyes on the human's.
"Queen of Evil." She mutters demurely.
The look of disgust that passes over Bill's face is almost enough to make the Mistress break character.
"She doesn't look very evil. " She says firmly.
The Mistress turns back to the piano.
"In fact- I would say she's the least likely person in this room to be evil. You're keeping her in a cage Doctor. In a glass cage. " The human lets out a ragged breath, sounding on the edge of tears.
"I'm protecting her." He says under his breath, voice low as he watches her play.
Bill scoffs.
" Protecting her? She's playing music at your command in a cage! Do you even know what this looks like Doctor?" Bill's voice trembles and- oh dear- the human is crying now. Crying over her. It's touching- it really is. The Mistress is almost laughing.
The Doctor is silent.
"It looks like slavery." She says horrified, "Doctor, it looks like slavery." The Doctor still says nothing and the song comes to an end, petering out into the sound of breathing.
All three of them are still.
The Doctor stands.
"Trust me Bill. Without hope. Without witness. Without reward. She is my friend." The Mistress hears him lift his arm.
"I have to go." He says solemnly. He turns and the Mistress does too. She stands from the stool softly, watching him leave. The human stares between them, heartbroken. She strides over to the glass separating them and stops beside the Time Lady.
"I'm not leaving her, Doctor." She says firmly. The Doctor stops for a moment and a sigh lifts his shoulders.
"She's dangerous Bill, more than you could imagine." He says, voice rough. Bill doesn't even look at the Mistress.
"You keep saying that." She bites back. Time stretches on, suspending them in uncertainty.
The Doctor breaks it.
"Please Bill. Be careful." He says, finally leaving.
The human looks at her, placing a hand against the glass.
"I'll get you out."
Something in the more damaged her from this new timeline reacts to this.
The Mistress feels her heart warm, hope blossom there in conflict with her old memories and self.
"Thank you." She whispers, pressing her hand against the glass, opposite the humans.
"Bill." She finishes, eyes intent on the young woman's.
