"You don't look like a coward. But all you've wanted to do is leave. You know so much about us..." The Doctor fakely says it's because they're so famous, but she knows there's more. He takes one look in those stern, lovely eyes, and knows she won't let it go. They keep working, and he tries to explain about fixed moments. "Tiny, precious moments. Everything else is in flux, anything can happen, but those certain moments, they have to stand. This base, on Mars, with you, Adelaide Brooke, this is one vital moment. What happens here must always happen."
She knows enough to get worried now: "Which is what?" He lies, twisting one way and another, desperate to be anywhere else, hearts moving in separate directions, every instinct screaming at him to run, leave, disappear, except the highest one of all. So he lies instead. "...I don't know." He looks at her face: "I think something wonderful happens." She swallows as he looks at her -- who she is, has been, will be -- and sees her all at once. The Time Lord's burden. "Something that started fifty years ago, isn't that right?" She stares; she's never told a soul. "You told your daughter. And maybe one day she tells the story to her daughter. The day the Earth was stolen and moved across the universe. And you...?"
He watches Adelaide remember. For us, it was only a year ago, when the planets were stolen and the skies replaced. Her father left her hiding in an attic, and went looking for her mother, and they both died. They were never found; this part makes the Doctor saddest. But while she was up there -- in the midst of extinction, flying just a little bit above it; waiting for her family that would never return -- she looked through a skylight at a Dalek, who stared down at her. Down on the streets there was panic, and burning, but up in the sky an alien inspected her, and looked right into her. And she looked up at it, and -- she nearly smiles, now -- it simply went away.
"I knew, that night, I knew I would follow it." But not for revenge, the Doctor can see. She still has tears in her eyes when she asks what the point of that would be.