'You used me.' The words seemed to echo and the Doctor had to look away, one hand reaching for the console as he felt the guilt bearing down on him. But his expression hardened when he managed to look at Jack again, giving a curt nod. "I did. I had to try."

The Doctor swallowed, not looking at the Master but feeling his presence all the more. "And if he had died then and there, what would it have changed? I know he's done unforgivable things, Jack. If I could undo it all, I would. If I could keep everyone safe forever..."

He trailed off, blinking once as he looked at the console, because between Jack and the Master it was the only neutral spot he could find. "I can't just keep losing all the time."

With that he turned fully to face the console, pulling a lever. "So. Cardiff, yeah? Or anywhere else? I'll take you anywhere, anytime. Just say."