He should have stopped her.
"I'm travelling, that's all. And then I'll come back."
He stood there, listening to the child comforting and reassuring the parent with simple words. Believing them to be true as she said them, with a child's trust, and a child's smile. He clutched the rucksack like a shield.
"Mum, if you saw it out there, you'd never stay home."
The Doctor wasn't good at domestics. He'd never been faced with a furious and terrified mother before, demanding he make promises he couldn't keep.
He'd spent the last hundred years deftly avoiding these situations. Side-stepping the worried mums and frantic fathers and sisters and cousins and wives and husbands like they were leaves being blown around the pavement by the wind, spinning in circles while he kept on striding forward. He saw Jackie coming, and he couldn't get out of the way fast enough. He would have laughed if the laugh wasn't sticking in his throat like a sob in its infancy.
He took in orphans. He took in stow-aways. He took in adventurers. He even, upon occasion, took in spies and saboteurs. Minders meant to hold him in check, and adults who got the stars in their eyes. His door was open to them. He held out the brass ring, knowing which of them would take it. Knowing before they even did. And still he offered, even though he knew.
He took in anyone in need. Anyone he thought could keep up with him, who shared a passion for never standing still when there were new horizons to be mapped.
But he'd never asked of them more than once.
He'd never needed them so badly, as he needed her now, which Jackie could see even if Rose couldn't.
Mothers know. So, to stay safe, he'd avoided mothers in particular.
"You still can't promise me. What if she gets lost? What if something happens to you, Doctor, and she's left all alone, standing on some moon a million light-years away. How long do I wait then?"
Another year? hung in the air between them in that split-second. Ten years?
Will my daughter come back to me older than I am?
Will my daughter come back to me at all? shone in Jackie's yes, and he almost flinched.
He couldn't promise, and they both knew it, even if Rose didn't or couldn't or wouldn't admit it.
It was Rose's choice to make, he'd lied to himself from the first. She was a big girl, and knew her own mind.
Which was why he kept dangling the Universe in front of her like a carrot on a string. Because he knew--he knew in his bones that she wouldn't be able to say no, once she'd got the merest taste of it.
Rose, as always, came to his rescue. Rose, barely singed from the missile. Barely bruised from the metal box they were sealed in crashing two stories to the pavement. Rose, who had shown up with a rucksack and a grin, even after he'd said what he'd said, the way he'd said it, forcing her to choose. Loving him for manipulating her, resorting to emotional blackmail, dangling the carrot.
"Mum, you're forgetting it's a time machine. I could go travelling around suns and planets, and all the way out to the edge of the universe and by the time I get back, yeah? Ten seconds would have passed. Just ten seconds." Her hands were on Jackie's shoulders, and she was still smiling, because she didn't know. Not yet. "So stop worrying. I'll see you in ten seconds time. Yeah?"
They had embraced, and even with Jackie's back to him, he knew she was weeping. And he knew Rose wasn't. Wouldn't. Because she believed it.
He couldn't bear to watch it.
He'd gone inside the TARDIS. He'd run away. Before Rose could see his face, and know what he knew.
She could die.
It had happened before. Sons and daughters like Katarina and Adric. Both of them children, barely Rose's age. Brave and clever and dead.
She could die.
She could change.
The girl Jackie was begging to stay could cease to exist. Could. Would. She'd be unable to be confined to a single planet, in a single moment, living a small life after getting even a glimpse of the vastness of his world. She wanted more, and wouldn't be satisfied until she had got it. She wanted more than this little world, this time barely out of smokestacks and steams ships, could ever give her.
He knew that. He'd already seen it in her. She was making a promise she couldn't keep. And even though Jackie had begged him to do the same he hadn't been able to force the lie past his lips. But Rose had no idea what she was doing. The torture she was inflicting out of love.
He could have stopped her. Told her anything. Reminded her about Cardiff, and Christmas every day as a pleasant fiction but perhaps not practical. Remind her about yesterday when it came to that. Sitting on a rooftop and I can't do that to her again and what short memories these humans have.
The TARDIS wasn't quite that reliable, he'd say.
Ten seconds is a bit like angels dancing on pin-heads really, and shouldn't we ought to just promise to send postcards at Christmas?
He could have stopped her.
Someday she could would look back on this moment, and realise that he knew that he'd known, that he could have stopped her, and despise him.
He should have stopped her.
Mum, if you saw it out there, you'd never stay home.
He knew better.
She's my daughter. She's just a kid.
He knew Jackie would stand there on the rain-slick pavement, counting backwards to zero.
He knew she'd spend the rest of her life, counting the seconds.
An entire life measured in ten second intervals.
And he should have stopped her.
But he didn't.