DUNBAR: Since you seem to have it all sewn up, Doctor, perhaps you can tell us where the pod is now?

DOCTOR: I'll make a guess. Right here, in this country. Action! Action, that's what we need. If we don't find that pod before it germinates, it'll be the end of everything. Everything, you understand? Even your pension!

DOCTOR: But the final responsibility is mine, and mine alone. Listen, if someone who knew the future pointed out a child to you and told you that that child would grow up totally evil, to be a ruthless dictator who would destroy millions of lives, could you then kill that child?

DOCTOR: Just touch these two strands together and the Daleks are finished. Have I that right?

DOCTOR: History sometimes gives us a terrible shock, and that is because we don’t quite fully understand. Why should we? After all, we’re too small to realize its final pattern. Therefore don’t try and judge it from where you stand.

DOCTOR: Even after all this time he cannot understand. I dare not change the course of history. Well, at least I taught him to take some precautions. He did remember to look at the scanner before he opened the doors. Now they're all gone. All gone. None of them could understand. Not even my little Susan, or Vicki. And as for Barbara and Chatterton. Chesterton. They were all too impatient to get back to their own time. And now, Steven. Perhaps I should go home, back to my own planet. But I can't. I can't.