"No-no-no-no!" The Doctor shouted as sparks erupted from the spin-down neutron colluder. "The arc-filter balance modulator's destabilising!" He ran around the mound of electronics and gave the repurposed mass spectrometer a sharp kick.
"What's going wrong, Doctor?" Martha asked, standing helplessly to one side.
"The spin-down neutrons are flying through the modulator, great, but then they're trying to flow out through the side of the density inversion controller!" he wailed. "And now the magnetic field's stuck, so they'll just miss the TARDIS completely!"
"But if you swapped that thing there round, wouldn't that reverse the polarity of the neutron flow?"
The Doctor looked round at her, eyes flashing. "Ros-" He looked up, caught himself, realised where he was. "Martha Jones, you are a genius!" he said, and gave her a brief half-hug.
Then he froze, solemn and empty, as memories crashed down on him. The last time he'd said those words. "Rose Tyler, you are a genius!" In his mind's eye, he watched again as he tricked her into leaving him; watched again as she came back, the Bad Wolf, the Time Vortex in her eyes; watched again as the was torn away from him, forever, sucked through the rift. Rose Tyler.
And Martha saw her in his eyes, and decided. It was now or never - she couldn't keep living like this, not knowing. "What happened to her, Doctor?"
He didn't reply.
"I know you don't want to talk about it, but I have to know. So what happened? Where is Rose Tyler?"
He looked as though he wanted to speak but couldn't find the words.
"Sometimes I feel like you just placed me beside you to take Rose's place, then when you get bored with me you'll just move on to someone else."
"It's not like that."
"But it is, though." Then Martha changed tack slightly. "And Rose wasn't the first, was she?"
The look on his face told all.
"No? I thought not. How many, Doctor? How many have you led to their deaths?"
"Rose isn't dead."
"But she's obviously as good as, or I wouldn't be here. 'Cos that's what you do, Doctor, you take hold of people. You could get anyone to die for you." He was making him sound like some sort of murderer, and part of her hated herself for it. Hated herself for the torture she could see in his eyes she was putting him through. She pushed it to the back of her mind as she recalled something else. "And you went and fell in love with Joan Redfern, and left me stranded. It's the same pattern, again and again. But if it wasn't for me, you wouldn't even be the Doctor any more, you'd be John Smith, and you'd be long dead."
He opened his mouth, but she didn't want to hear it. She turned and ran, to the first safe haven she could think of.
"Martha!" he yelled through the blue doors. There was, unsurprisingly, no reply. He tried the door, but is stayed firmly shut. He inserted his key into the lock, but it refused to turn. The TARDIS had locked him out. The Doctor's shoulders slumped. Why was everyone turning against him?
Martha was lost. She knew the TARDIS was bigger on the inside, but never before had she appreciated just how much bigger.
She stepped through a small door at the back of a dark, low ceilinged room full of boxes of what appeared to be spare parts for the TARDIS, and froze. She had appeared in a huge, wooden panelled room like a concert hall. It was completely and utterly empty apart from a pristine-looking grand piano at the opposite end. Her footsteps echoed endlessly as she made her way over to it.
She was surprised to find two sheets of handwritten piano music on the stand. The handwriting was familiar, but she couldn't quite remember where she'd seen it before.
Then Martha remembered the journal John Smith had written about his strange dreams of the Doctor. So this was the Doctor's handwriting, and the Doctor had written this piece. She sat down and played a few random notes. She had attained Grade 8 piano the year before starting university, but hadn't really played since then. Well, now was as good a time as ever to get back into practice…
As she started to play, something sliced into her mind like a knife - a memory, playing like a film in her mind's eye. It wasn't hers. The feelings this memory expressed were so different, so alien, that there was only really one person they could belong to.
She was watching the Doctor's memories.
She watched through his eyes as he met Rose Tyler for the first time, a young shop assistant cornered by Autons, but oh, so much more than that. She watched as Rose declined, then accepted his offer, and left her mum, her boyfriend, her life, to travel through time and space, to her father's death, to the end of the world, to World War Two London, to save the world, countless times. The Doctor was different, then, but the same.
She watched as Rose was captured by Daleks, rescued, then unwillingly tricked and sent home. She watched as Rose came back, and as the Doctor saved her from the power of the Time Vortex; in his eyes, Rose Tyler was more than worth dying for. She watched as the Doctor became the man she knew and loved.
And through him she discovered that Rose had had competition - Sarah Jane Smith, Madame de Pompadour - women who had thought, or wished, that the Doctor was theirs alone. But he never would be, she realised; they all just had to make do with whatever part of him they got at the time, and make the most of it, because it wouldn't be theirs forever. Far from it. But despite all that, it was worth it. It was utterly, gloriously worth it.
She watched, through the Doctor's eyes, the Battle of Canary Wharf. She watched as once again, Rose refused to leave, no matter what. She watched as Rose Tyler was torn away from her Doctor, sucked irreversibly into a parallel, Doctorless, universe. And Martha understood.
With that understanding came the realisation that she was alone once more inside her own mind. It had been like a movie trailer - tantalisingly short, showing her enough, but no more. She wondered how she'd been allowed to view the memories, and if the Doctor knew about it. She seriously hoped he didn't.
"He doesn't. Don't worry," came a voice, female and friendly, somehow both inside and outside her mind. It almost felt as if it was coming from… the TARDIS itself.
"But that's impossible," Martha muttered.
"All your time with the Doctor and you still think 'impossible'," the TARDIS drew the inverted commas with her voice, "exists? Oh, my Martha, you still have much to learn."
"You're alive?"
"Of course."
Martha didn't know what to think, or say. She should have guessed.
She looked at the music again, played it right the way through. It was so simple, but so beautiful. Bittersweet and Gallifreyan. Love and loss. The Time Lord's lament.