Two TARDISes side by side in the lab. Or rather, the same TARDIS twice.

If he wanted, he could dash into the one that works. It is, after all, just as much his as the crippled one. And then he'd be free again, loosed from this planet-bound, time-bound prison.

But he couldn't play such a dirty trick on his old self. UNIT and its guns haven't made him that ruthless. Not yet.

"Well, goodbye," he says. "And thanks." Nine-tenths of this world's population would be infected with the alien virus by now, dying of it, if his old self hadn't happened (by one of those non-coincidences that are so common in his life) to turn up in his functioning TARDIS. The anti-viral is only produced in one small system of a galaxy ten thousand light years from earth.

A five-minute jaunt in the TARDIS. Easy, if you've got one.

"My pleasure," says his old self. Strange, what a shock it was a few months ago to not see that face in the mirror. He's long since realized what an improvement the new body is. Taller, slimmer, stronger. Handsomer, too, he decides now.

There's a four-voiced chorus of goodbyes. Zoe waves and steps into the TARDIS, followed by his old self. Jamie smiles and turns. It's a cheerful, unshadowed smile, not at all like the last time they said goodbye forever.

"Wait." He grabs Jamie's arm and leads him a few steps away from the open TARDIS door. "Jamie, would you like to stay?"

"Stay? But - "

"I know it's not your own time. But it's better than your own in a lot of ways." Safer. The slaughter after Culloden is two hundred years past. "And of course if I get the TARDIS fixed--when I get it fixed--we'll be able to go anywhere." Proper travel with no meddling, nothing to bring the Time Lords down on him again. He can do that, for one little human lifetime.

Jamie looks up at him--oh, that is odd, he's not used to that--with his eyebrows scrunched together in confusion. "Doctor - "

"Please stay," he says. Behind Jamie, his old self stands in the TARDIS doorway, watching this silently. "I've missed you." This is both a complete truth and a partial one, like the infinite set of all integers that nestles within the infinite set of all numbers.

"Oh, Doctor." Jamie puts a hand on his shoulder, the old familiar way, although now he has to reach up to do it. "I couldn't. I'd miss him. You. Och, you know what I mean."

"Yes, of course." He doesn't say that they won't have much longer together. That if Jamie doesn't stay he won't be able to miss his Doctor. That the only possible future for them starts now.

Don't cross your own timeline. It's one of the great Time Lord laws, and as such he's never much cared for it. But he's beginning to understand it. It's not to protect the fabric of time, which knits itself up readily enough. It's to stop you bashing your head bloody against the great mountain of things you want to change, but can't.

"Before you go," he says, and hesitantly touches Jamie's cheek. "Would you mind if I - ?"

"What? Oh." Jamie grips his shoulder a bit harder. "All right." He lifts his face and lets himself be kissed.

For a little while, perhaps a minute, the Doctor holds him in one slow kiss. He doesn't try anything persuasive with his tongue or the hand that rests on the rough wool over Jamie's hip. This is not the time. This is not the time that is gone.

He doesn't say goodbye. Jamie turns from him to the man in the TARDIS doorway, and they whisper, leaning together. Then Jamie walks in, out of sight.

"Don't ask," he says to the man he used to be.

"No." Sadly. His old face was a good face for sadness. Quite unnecessarily so, because he was happy most of the time. "Look, I'll take very good care of him. I promise."

"I know you will."

A nod is answer enough. Then the TARDIS door shuts and the sound of dematerialization begins, the harsh and wonderful sound of possibility.

He closes his eyes so as not to watch it disappear.