Disclaimer: I don't own Doctor Who, the Doctor or the TARDIS (did you know the BBC actually trademarked the word TARDIS?)
1: Fixed Point in Time
As the sound of the TARDIS engines faded away from Bad Wolf Bay, the Doctor - now John Smith - turned to Rose Tyler and grinned.
"So," he said. "Life as a human!"
"I now pronounce you man and wife! You may kiss the bride."
John and Rose Smith were happy to oblige.
Later, they had a laugh about the vicar's phrasing, just the two of them.
"What would they have said if I'd married you as an alien?" grinned Rose. "Alien and wife? Time Lord and wife?"
John snorted. "If we'd actually told the vicar you were marrying an alien, I doubt there would have been a wedding at all. He'd think we were crazy!"
"Quite a lot of people think you're crazy anyway," Rose reminded him.
"But not you?"
He suddenly looked so worried that Rose bent to kiss him without thinking. "Of course not," she reassured him, after the kiss.
That night, as they lay in bed together, John looked over at his wife and smiled.
"You know," he whispered, "you don't look any different to the day we first met."
He expected her to thank him with kisses, or to start reminiscing about that first time, or maybe to make a cheeky comment about how she couldn't say the same for him because he'd regenerated since then. But Rose said nothing, and John realised that she was actually giving this matter serious thought.
"I know," she said finally. "The woman in the corner shop asked me for proof of age the other day. She wouldn't believe I was over 21, isn't that weird!"
John frowned. "I didn't mean it literally," he said. He hadn't thought that through before he said it, and hoped Rose wouldn't take it as an insult, but she seemed too busy thinking about the problem of her age.
Which, now he thought about it, was strange. Very strange.
Rose nodded to herself. "This world's been running ahead of… of the one you were in. The one the alien Doctor's in now. I was gone for two years for you, but it was three for me. And you lose track of time inside the TARDIS, but I bet we spent at least a year travelling together. Maybe more. That makes me officially twenty-three or so, and yet I still look like a nineteen-year-old. Exactly the same as when we first met."
"Not when we first met…" murmured John, reaching up to touch the scar at the base of her neck, acquired in 1336 Japan when a man held a knife to her throat. "Exactly the same as…" No. Oh please no. Not this, not now!
He closed his eyes, accessing a certain part of his mind. A Time Lord part. The part that warned him of things that shouldn't be there, things that were wrong. He'd shut it off after running from Captain Jack back in the year 200100, knowing that they'd cross paths again some day.
The scar on Rose's neck happened just before we ended up on the GameStation. And I shut off that part of my mind while Bad Wolf was there, just after Jack woke up. So that means…
Please, in the name of Rassilon, let me be wrong!
John activated that part of his mind again, just for a second, just to check whether he was right. And of course he was.
"Exactly the same as you were just after Bad Wolf left," he whispered finally. His voice was so soft Rose had to lean close to hear it. "You haven't changed at all since then. You haven't aged, you haven't been injured -"
"I have," Rose corrected him, also whispering. "Lots of times. Working for Torchwood."
"But it hasn't left any scars," John continued. "You've healed quickly, too. Survived things everyone thought would kill you."
Rose pulled away from him. "How do you know?" she breathed.
"I… you remind me of a friend of mine," he told her evasively. Please, he willed her silently, don't work it out. Let me have this time with you.
But she did work it out, of course. Rose was brilliant; he'd always said that.
"You mean Jack," she murmured. "You're saying Bad Wolf made me like Jack."
Then it started to sink in. "I'm a fixed point in space and time!" she choked. "Oh god, you must hate me! I'm wrong, like you said Jack was!"
John took her in his arms and let her cry on his shoulder. "No, no," he reassured her. "I've shut that part of my mind off now. You're just another human to me… well, no you're not, you're my wife!"
Please, don't realise it. Please…
Rose gave a shaky laugh. Then she froze, horrified.
"Just another human…oh god! You're human now! You're human - and I'm not!"
Another time, John decided, he'd have appreciated that irony. Their positions were reversed. But he knew what Rose would do now, because it was the same thing he'd done, when he was the Doctor. She would distance herself from him, because she couldn't bear to watch him fade and die.
"You can spend the rest of your life with me," murmured Rose, remembering what John as the Doctor had told her in that school. "But I can't spend the rest of mine with you. I have to live on."
John sighed. "So you understand," he said dully, and got out of the bed, reaching for his dressing-gown. This has to be done.
Rose stared after him in bewilderment. "But… where are you going?"
"I don't know," said John bitterly. "Anywhere. Everywhere. You won't want to watch me grow old. It's better for you if I distance myself while I can."
"No!" snapped Rose. "I'll tell you where you're going: nowhere. You're staying right here, with me."
John stared. "But -"
"I just told you, John. You can spend the rest of your life with me. We've both waited too long for this, far too long. And you're not running away again!"
John smiled down at her, slipping back under the covers. "I'm not going to run away, Rose," he whispered. "Not from you, not any more."
And he leant in and kissed her, and didn't care about the consequences, and nor did she.