"I always thought it was odd," Lorna had said, "that alien beam. She said that it was making people angry, but we wouldn't need that, would we? There's so many reasons why anyone'd be angry now. But the Doctor would never see that, I don't think. No matter how often people said, she'd never, ever see. She'd think it was… aliens in the water supply, or something. Anything to think things weren't as bad as they really were."
She looked up at the tree, whose expression was unreadable.
"That's the answer. It isn't causing it. It isn't causing anything at all. It was just us, all along. It was always us."
The Fleurlis was shaking his head, and Chris knew exactly why.
"That isn't it," she said. "Not quite."
She felt uncomfortable as her mother looked at her.
"The Doctor said something a while ago," she said hesitantly. "And I remembered it, because it didn't make any sense. That if something worked one way you might be able to flip it around, and somehow it would work just as well.
"The Doctor lies," said the Fleurlis in its unknowable voice.
"I know. But sometimes she tells the truth. So I thought maybe she was telling it this time, and more of it than she knew. There was a ray, or something, coming from here to the Earth. And it was breaking everything, because it was coming from a very dangerous place. But it didn't seem dangerous, when we saw it. It didn't seem much of anything at all. So what if it wasn't coming from there? What if the place she'd thought it was going was the place it was coming from all along? What would happen if you turned things around?"
She frowned.
"What if you reversed the polarity?"