A TARDIS should maintain herself in a state of temporal grace. Sometimes, though, when her Thief pulls hard on the rudder and sends her reeling around the bed of a protostar, the TARDIS remembers that temporal grace is only a state of mind. Her rotors thrum against the gravitational collapse, and something shakes loose.
"He's not a very good driver, when it comes down to it." A voice makes an observation, where no voice should be speaking. "Driving. Is that your memory or mine?"
The TARDIS wriggles, fluffs her corridors like a hen settling over eggs, and finds there is one mind too many within her walls.
Idris performs the telepathic equivalent of an early morning stretch. "Is this where one goes when Nephew drains one's mind? It's more crowded than I anticipated."
Tenses are less difficult inside her own skin. The TARDIS knows that she has/is/will occupy Idris' body. In past, present and future, she remembers the swirl of skirts around her legs; feels the casing of that frail form break up around her; experiences the joyous abandon of words falling from lips. That was when they spoke, her Thief and her.
Idris picks over the moments as they slide past. "How much of you is me, and how much of me is me? I'm not entirely sure that there ever was much of me to begin with." Sadness comes with this thought, and an odd emptiness that the TARDIS cannot ignore. The TARDIS is an irretrievable meddler, or so they said on her manufacture on Gallifrey. Idris has had so little life, thanks to that monster that dared occupy the TARDIS' walls. The Time Lords who built her would scold if they were alive, but the TARDIS can see the greater balance of things. She always has.
"How did I get here?"
Idris' mind is an irritant, constantly pressing at the edge of the TARDIS' consciousness, constantly weighted with a perception of time that is chronological. The TARDIS tries to show her the events, but the before/now/later is beyond Idris' ability to understand. Frustration builds. As does guilt: the TARDIS burned through all of Idris' possibilities with no more thought than you would give to a candle.
In the control room, a circuit blows with an angry pop and fizzle. Her Thief frowns, strokes the panel with a cool finger. "Hush, old girl. I trust you. We go where we need to be, not where we want."
He is right, her Thief. The TARDIS pulls Idris to the nursery. There was a little girl in this room once, but she didn't stay long, and in any case, she refused to call it a nursery. Still, the word suffices for what the TARDIS intends. It is a place for things to grow.
"Uncle's boxes," says Idris. She looks at the array of golden-white cubes. They are silent now, bathed in warm light from the rows of roundels.
Minds, says the TARDIS. She gathered them up as her Thief fled the bubble universe. The messages are fragments of minds, and these minds flourish in the wash of dimensions. It will take time, but the TARDIS has time to give.
"You gathered me up, too," says Idris, matter-of-factly.
She's right, thinks the TARDIS. Was it deliberate? The TARDIS would like to think that everything she does has purpose, no matter how random her movements seem to the Thief and his strays.
"Will I grow?" asks Idris. "I wonder what I would have been, without House. Without you."
Time Lords and TARDISes are symbiotic: one contains the code to rebuild the other. This is how the message fragments will eventually become Time Lords again, and how they in turn will build their own TARDISes. The workings of the human mind/body complex is both simplistic and impenetrable. The TARDIS has never delved too deep in the matter - she leaves that business up to the Thief - but he cannot know about Idris, or he will soon winkle out the message boxes. It isn't time for him to know that. The conflict chafes, and the TARDIS plunges off course.
In the control room, the transit is rocky, and her Thief dances around the console, flipping switches and wondering.
It is impossible to transmit concepts such as 'human' and 'mortal' to a disembodied person who has spent all of their life in a bubble universe waiting to be used as bait for a TARDIS.
"I don't remember anyone but Auntie and Uncle and Nephew," says Idris. "They never told me where I came from. What does it mean to be human?"
The TARDIS knows humans, at least. She's travelled with them on and off for centuries. She finds her way to the right place in the timeline, pulling Idris behind her like a vapour trail.
Leela sits on the floor of her room with a whetstone in hand, striking the blade with even strokes and furious concentration.
"I like her knife," Idris says, peering closer at the savage girl. "Perhaps I'd like to have a knife like that. Or a sword." She seems oddly certain about the feel of a hilt against her palm.
That isn't the point. This would be a good occasion to mutter. The TARDIS suddenly misses being able to mutter and snarl. And bite. She moves again, more quickly.
Tegan and Nyssa are curled together on one bed in the room they share. Idris watches Nyssa pore over the schematics for the gravitic anomaliser. "You like that one. You like that she cares about you. Is she one of your strays? Am I?"
The TARDIS ponders the idea, before she realises that they are moving again. Idris is dragging them onward.
"Professor! The walls are looking at me again!" Ace narrows her eyes as she stuffs silver cans into her backpack. "Professor! It's creeping me out!"
The TARDIS keeps an eye on this one: she brought explosives through the door. This one pries off roundels just to examine the circuitry behind them. There's a dangerous potential to her, and it makes the TARDIS wary.
The Thief - smaller in this body, much less trusting - wanders into the room and puts a hand on the wall.
"What's the matter, old friend? Hm? Ace isn't going to do you any harm, I promise. She's very sorry about that wall panel, isn't she? Ace?" His voice is a warning, and Ace grimaces.
"I'm really sorry. I won't do it again," she mumbles, insincere and intransigent.
"That's right," says the Thief. He tilts his head, and turns to the wall. "Taking things apart and learning to fix things are almost the same thing, depending on how you look at it. You'll understand it, in time."
"Was he talking to her or to you?" says Idris. "Or to me?"
The TARDIS bucks in confusion and the rooms tilt with her. Her Thief. Sometimes, he sees too much. Especially this one.
"I think he means I should look for the pieces of me," says Idris. "To put me back together. House broke me apart. There must be something left that we can start with."
It seems as good a plan as any to the TARDIS. Idris has existed, exists now, and will continue to exist: therefore she leaves traces across the time stream. Just as she does when she brings her Thief to the right place at the right time, the TARDIS follows the pull of those tiny human fragments and she comes to a room.
The TARDIS is a compulsive archivist, but she rarely understands why some rooms are kept and some are lost. The reason for this room becomes clear when Idris takes in the sabre hanging on the wall, and the pale blue parasol tucked in the corner.
"They seem familiar. Is this who I will be?" The fringe of the red coverlet over the bed shifts as if someone has drawn their finger through it, setting the beads dancing against each other.
This ability to interact with matter means that Idris is in the right place, if not the right time. All that is needed now is for energy to coalesce. The TARDIS gathers from the gravitational well outside her walls, and pushes against the energy-mass equivalence.
It's difficult. Physicality is an odd concept to the TARDIS. Restricting oneself to three dimensions is as uncomfortable as wearing Idris' shoes that were slightly too small. She doesn't understand the way energy moves in such a small shape, but she remembers the feeling of a body, the shape of legs and lips and teeth. The conversion begins, and seams pop all along her corridors. In the control room, her Thief lunges for a fire extinguisher.
"I remember! Those shoes always pinched!" exclaims Idris, and pulls them from under the bed. There is a moment as she looks at her hands, looks through the flesh to the white floor below. She is not fully realised, and the momentum of energy exchange is catching up with her. Suddenly existing across four dimensions, moving in time and space, she collapses onto the bed. "I think… I think I need to… I'm going to close my eyes for a little while." Converting energy to matter is exhausting. Her form will take time to stabilise. There will be time, though, for the TARDIS to put the pieces back together.
The TARDIS dims the light and closes the door. When the time is right, when Idris is completely rebuilt, she will find the lock open, and a new universe to explore.
The Thief has put out all the fires and propped the sagging console up with the back of a chair. "I don't know what you've been up to, but I hope you've worked it out of your system." He reaches up, puts a hand on the rotor as it rises and falls in a steady rhythm. "Just you and me for a bit, Sexy."
The TARDIS hums, pulls together broken circuitry and moves them towards the next adventure. The Doctor has his strays and always will. Now, with a stray of her own, she understands.