How Martha found out about regeneration
The doors closed, the Doctor hit the dematerialisation lever, and the TARDIS shuddered into motion.
"Just us again, then," he said, fake cheeriness plastered all over his face. "Where d'you want to go?"
"Home," said Martha, gently, sitting down on the seat by the console. "I need to see my family." She did not feel this was the time to tell him she would be following Jack Harkness's example and leave too. "But slowly," she added, as he went to punch in the coordinates. "No rush."
The Doctor gave her a smile and pushed a different button. "We'll orbit for a while, then. Tea?"
"Talk," Martha replied. "We haven't had the chance, what with " She tailed off. She meant, what with the funeral and the clean-up and dealing with UNIT and the government, and repairing the TARDIS; and in any case the Doctor had clearly not been in a talking mood for many days. "With everything," she ended.
"No." He folded his arms, perching on the edge of the console. "What do you want to talk about?"
"Time Lords," she said.
He rubbed his brow. "Martha I "
"No, you don't," Martha said, firmly. "Not this time. Anyway, it's just one question. When Jack - when Jack saw you, at the end of the universe, you were talking about regeneration. He said you had a new face. And then with with him," she found she still could not quite get out the Master's name, "you told him to regenerate. Just a bullet, you said."
"That's not an answer," said Martha.
The Doctor looked past her, eyes staring into - what? She could not tell. "It's our way of cheating death," he said.
"Time Lords are immortal?"
"No. Not immortal. Not like Jack, either. Our cells have the capacity to literally regenerate. In the case of severe injury, or very old age, my body will rewrite itself. New shape. Old memories."
Martha digested this. "Completely?"
"So this isn't your first body?" She wrinkled her nose. "God, that sounds weird. Even after everything we've done, that sounds weird."
"I beg your pardon?" Martha said, caught aback.
The Doctor shrugged. "This is my tenth body. Or ninth regeneration, depending on how you look at it. I did quite well in my first - got quite a long way in that one. Since then I've had an alarming propensity to rattle through bodies like they're going out of fashion. Last time around it was barely an Earth year." He gestured at the hand bubbling away in a jar at his feet. "I was able to regrow my hand because I was still in the regenerative cycle."
Martha got down off her seat and squinted at the hand. "All your cells?"
"So, if you get old, or if you're fatally injured."
The Doctor's voice was ironic. "Traditionally the former. But I've never liked tradition."
"How often can you do it?"
He turned, and began fiddling with dials, avoiding her gaze. "They say twelve times. Thirteen bodies. Like I said, I'm rattling through my lives. Reckless, that's me."
Martha stood, her legs complaining. "Ow. But you don't have to do it, right?"
Pulling his glasses from a pocket, he squinted at a screen. "Eh?"
"Doctor, you heard me."
"You know the answer. You watched him refuse."
She looked down at her hands. "Yeah. Mind over body, I suppose. I've seen that with patients - some people just give in if you tell them they have cancer or whatever. Others will fight and fight. I guess he was the giving in type."
The Doctor turned, taking off his glasses, and looked at her properly, meeting her gaze with eyes that were ancient and full of a deep grief Martha knew she would never be able to fully understand.
"No. It wasn't a case of giving in. He chose death because it meant he won. He knew what it was like, to know Gallifrey's gone, to know everyone's lost. But all he ever really cared about was power - that was all he cared about even when we were young. Power over me. And in the end, he won. I lost." He waved an arm, gesturing at the golden light of the TARDIS. "We're back to where we started. This is all that's left of Gallifrey, one battered old Type 40 with a broken chameleon circuit and an equally battered old Time Lord on his tenth life. Not much, is it?"
Martha found herself blinking back tears. She moved forward and put her arms around him. "It's better than nothing. So much more than nothing. But maybe you should start looking after this body of yours. Not sure what we'd do without you, us stupid humans."
She felt him grin into her shoulder.
"Oh, there're plenty of people to look after the Earth," the Doctor said, giving her a tight hug and stepping out of the embrace. "The Jones family, for a start. Time to go and see them?"
"Yeah." Martha nodded. "Yeah, I think so."
He got to work, moving around the console. For a few moments she watched him, before quietly leaving. There were bags to be packed; for though he had lost, so had her family, and they were the ones who really needed her now.