Ellie: You kept it.
Dave: Of course I kept it.
Dave: Cause this exact leaf had to grow in that exact way, in that exact place, so that precise wind could tear it from that precise branch and make it fly into this exact face, at that exact moment. And if just one of those tiny little things had never happened, I'd never have met you. Which makes this the most important leaf in human history.
Clara: I've never been here before. I've never been anywhere like it before. I just saw a little girl who looked like she needed help.
Clara: Really really.
Merry: Can you help me?
Clara: That's why I'm still here.
Clara: Why are we walking away? We can't just walk away. This is my fault, I talked her into doing this.
The Doctor: Listen. There is one thing you need to know about traveling with me. Well, one thing apart from the blue box and the two hearts. We don't walk away.
The Doctor: Okay. Let me go.
Clara: I can't.
The Doctor: Try, you have to.
The Doctor: Because it really hurts.
The Doctor: Oh, that is interesting. A frequency-modulated acoustic lock. The key changes ten million zillion squillion times a second.
Clara: Can you open it?
The Doctor: Technically, no. In reality, also no. But still, let's give it a stab.
Clara: Did you just lock us in?
The Doctor: Yep.
Clara: With a soul-eating monster?
The Doctor: Yep.
Clara: Is there actually a way to get out?
The Doctor: What, before it eats our souls?
Clara: Ideally, yeah.
The Doctor: Possibly. Probably. There usually seems to be.
Clara: Stop it, you're scaring her.
The Doctor: Good, she should be scared. She's sacrificing herself, she should know what that means. Do you know what that means, Merry?
Merry: A god chose me.
The Doctor: It's not a god. It'll feed on your soul but that doesn't make it a god.
The Doctor: Hey, do you mind if I tell you a story, one you might not have heard? All the elements in your body were forged many, many millions of years ago in the heart of a faraway star that exploded and died. that explosion scattered those elements across the desolations of deep space. After so, so many millions of years, these elements came together to form new stars and new planets. And on and on it went. The elements came together and burst apart, forming shoes and ships and sealing wax, and cabbages and kings. Until eventually they came together to make you. You are unique in the universe. There is only one Merry Galel. And there will never be another. Getting rid of that existence isn't a sacrifice. It is a waste.
Clara: You're going to fight it, aren't you?
The Doctor: Regrettably, yes, I think I may be about to do that.
Clara: It's really big.
The Doctor: I've seen bigger.
The Doctor: Are you joking? It's massive.
Clara: What about that stuff you said? "We don't walk away."
The Doctor: No, we don't walk away. But when we're holding onto something precious, we run. We run and run fast as we can and we don't stop running until we are out from under the shadow.
The Doctor: I have lived a long life and I have seen a few things. I walked away from the last great Time War, I marked the passing of the Time Lords, I saw the birth of the universe and I watched as time ran out, moment by moment until nothing remained. No time, no space, just me. I walked in universes where the laws of physics were devised by the mind of a madman. I watched universes freeze and creations burn. I have seen things you wouldn't believe. I have lost things you will never understand. And I know things, secrets that must never be told, knowledge that must never be spoken… knowledge that will make parasite gods blaze! So come on then! Take it!
Clara: This, the most important leaf in human history. The most important leaf in human history. It's full of stories, full of history, and full of a future that never got lived. Days that should have been but never were... passed on to me. This leaf isn't just the past, it's a whole future that never happened. There are billions and millions of unlived days for every day we live, an infinity, all the days that never came.
The Doctor: Because there's quite a difference, isn't there, between what was and what should have been. There's an awful lot of one, but there's an infinity of the other. And infinity is too much...