"Need to scan for alien tech." The Doctor lurched across the room to the console and started hitting switches and buttons of all sorts. He reached for the monitor, bringing it around to where he could easily read the output while he manipulated the controls. "If there's something here that's powerful enough to sidetrack a TARDIS and snatch my companions out of their proper timelines, then there might be something powerful enough to reverse the effects of lethal radiation poisoning. Just a guess, mind you, but I hope it's a good one. If it isn't ... " He paused in his work to glance at Donna, expression grave. "What that girl--Amy, you said?--told you about me changing my face, it's called regeneration. It's a trick Time Lords use when we're dying. Did you say death's grandaughter is here? And her name is Susan? Really? My granddaughter's name was Susan."
The Doctor paused, frowning, and was silent for a long moment before he shook off thoughts of a young woman he'd left behind to care for her human family oh so long ago. "But that's not important. What is important is that unless I do something drastic, and quickly, I'm going to change. If that happens, Donna, you have to promise me that you'll do what I say. No questions asked."