Margaret Blaine, The Doctor and others in “Boom Town”

I promise you I've changed since we last met, Doctor. There was this girl, just today, young thing... and something of a danger. She was getting too close. I felt the bloodlust rising, just as the family taught me. I was going to kill her without a thought. And then... I stopped. She's alive somewhere right now. She's walking around this city because I can change! I did change! I know I can't prove it--

I believe you.

Then you know I'm capable of better.

It doesn't mean anything.

I spared her life!

You let one go, but that's nothing new. Every now and then, a little victim's spared. Because she smiled, because he's got freckles, because they begged. And that's how you live with yourself. That's how you slaughter millions. Because once in a while, on a whim, if the wind's in the right direction, you happen to be kind.

Only a killer would know that. Is that right? From what I've seen, your funny little happy-go-lucky life leaves devastation in its wake. Always moving on, because you dare not go back. Playing with so many people's lives - you might as well be a god. And you're right, Doctor. You're absolutely right. Sometimes... you let one go. [almost tearful] Let me go.