Disclaimer: How I wish I owned them! Anyway, I don't; they're the property of the BBC.
He puts the TARDIS into the Vortex, and lets her hover. It's too soon, right now, to go anywhere else. He sits down, rests his feet on the console, and closes his eyes, letting himself sink into the timeless hum of his ship's engines.
"You've still got ash in your hair." Donna's voice, cutting through the noise. He opens his eyes; she's towelling off her own hair and is back in 21st-century clothes.
Shaking his head, he discovers she's right; grey ash showers down into the grating. He brushes it off his shoulders.
"You should shower, or something. You're not allergic to showers, are you?"
"Just aspirin." His voice sounds hollow, even to himself, and he makes an effort. "Don't ever try giving me aspirin - won't cure a headache, might kill me. I'll " he gives up. Donna isn't that easy to fool, he's realised that already.
She perches on the rail. "You saved the world," she says.
"We saved the world," the Doctor corrects her.
"But all those people "
"We made the right choice," he says. He's sure of that; the timelines are flowing smoothly, without disturbance. "Doing the right thing, it's not always easy."
Donna hangs the towel over the rail and begins to comb her hair. He watches her. It's good, to have someone to watch.
"How did you how many " she falls silent for a second, and then, lowering the comb, meets his eyes. "How many, when it was your planet?" she asks. He gets up, finds a loose wire, starts fiddling with it. "Doctor."
"Everyone. Millions. I had to do it, Donna - it wasn't just the world at stake, it was everyone's worlds. The universe. If they'd won " He stares emptily at the rotor. "I know it was the right thing to do, the only thing to do. I could have stopped it, you know, years ago, centuries ago. I had a chance, just one chance, to end it all before it began, and I failed."
Picking up the loose wire, he remembers holding those two thin ends in a corridor on Skaro, remembers hesitating, debating, over what? A roomful of Dalek embryos. He's changed, so much - now he would have touched the wires together without a moment's hesitation. He looks up, at Donna.
"Because I made the wrong choice, once, the right choice was so much harder when I had no choice." Getting out the sonic screwdriver, he solders the wire back into place. "And I can't go back to fix it. That's why Gallifrey had to die. That's why Pompeii died."
She nods. "Yeah. I get it, now. Not all a barrel of laughs, this time-travelling lark, is it?"
He manages a smile.
"I could do with a cuppa," Donna adds. "Want one? Too much sugar?"
"Thanks," he says, and she disappears with towel and comb in the direction of the kitchen. He hopes she knows he doesn't mean thank you for the tea.