This is the end. The Doctor's life will be a book that stops just pages into chapter two, and its last words will be "he failed." He's failed them, Jamie and Zoe, lost them most of lifespans that, being human, were already too short.
"Lie down," he says. "Breathe slowly." He's reserving the dregs of the last oxygen cylinder for them, pretending there's hope. Do they trust him still, or are they pretending too?
Even with extra oxygen, they'll die more quickly and easily than he. For some minutes he'll lie next to their corpses while his hearts struggle. He'll be conscious for most of it. If he's very unlucky, he'll regenerate once or twice before his body loses the capacity.
I want to go home, he thinks. I wish I'd never left. It's not true, but for an instant he believes it.
Are they thinking the same thing?
He lays his head in Jamie's lap. And that is perfectly simple after all, perfectly easy and right. Not even Zoe seems to find it odd.
Jamie touches his hair.
If only there had been a little more time. Time is as precious as oxygen, and now it has run out.