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"What do you mean?" asked Donna, resolutely not looking up from the assorted space junk in front of her, hoping her brother would let the subject drop.
"You know what I mean."
Of course she did, but could he blame her for wanting to avoid the subject? He was doing the same, really: refusing to say it aloud, as if that would somehow mean it wasn't true. He'd checked the records, though; he knew it had happened. And he always had to know all the facts.
How could three children break open a rift in time and space?
The question hung, unspoken, in the air between them.
"In telepathy," Donna said finally, "do you know what the most important thing is? Belief. If you believe you can do something - and if your willpower's strong enough - then you can do it. If you don't know that something's impossible, it isn't."
She fell silent. Harold was silent too. Waiting.
"I don't normally remember my dreams," she said next.
Harold blinked at the non sequitur, but his sister continued.
"I suppose I should've known it'd be important, but… The ones I do remember, they tend to be about Dad's past, and… I didn't think it was anything special. I don't know. We'd had an emotional day. Maybe my control isn't as good as I think it is. It always slips a bit in my sleep anyway."
"So you pulled me and Freya into your dream accidentally."
Harold knew her well enough to guess what she had been going to say, and even to jump to a conclusion which she had been avoiding. Sometimes Donna wished he didn't.
"Probably," she admitted. "It might not have been my dream, but we all ended up having the same dream, which must have been my doing."
"A dream about Gallifrey."
"Yes… Gallifrey." Now she looked up, for the first time in this awkward conversation, and met his eyes. "Do you want to see it?"
"Gallifrey? Of course." He didn't have to think about it; his answer was obvious to him. "Why? Don't you?"
Donna sighed. "Of course I do. That was what that dream was about, you know. I want all three of us to see Gallifrey - just once."
Another pause. Harold had worked out what she was doing now. She had jumped straight to a possible answer, realised intuitively that it was the right one, but didn't know how she'd got there. Now she was working backwards, filling in all the gaps.
"Of course you want to see Gallifrey, once you've thought of it," she continued distantly. "But you just haven't really thought about it - about what that means. I'm sure Freya's the same. And if you're offered an opportunity - you don't question it. Especially not in a dream."
"You've lost me," Harold admitted.
"Is it possible, getting to Gallifrey?" she demanded.
"Were you thinking that when you were dreaming about it?"
"No," he replied, and realised what she was talking about. "I didn't know it was impossible! Like you just said!"
"It didn't even cross your mind!" She made it sound ridiculous. Despite himself, he smiled.
"What about you?" he asked. "Did you know it couldn't be done?"
"In theory, yes." She smiled wryly. "I knew it was in a whole other universe, and inside a time-lock, but… I'm a mind-reader, Harry! My dad's an alien! I didn't believe in impossible!"
"Didn't?" Harold, ever the pedant, picked up on that one word, where most would have overlooked it. "Past tense?"
"We had the belief," Donna answered slowly. "All three of us together - because you overthink everything, so if you didn't see it Freya definitely wouldn't've. Belief and willpower, that's what it takes - enough to reach through the Rift, to try and force our minds into another universe… well, we managed that part, anyway. But breaking a time-lock? It might as well be impossible, the strength of mind it'd take to actually do it! It'll never happen!"
"So instead, we woke up feeling cheated and forgot to close the Rift behind us," Harold completed, deliberately turning it into a joke.
"Exactly," agreed Donna, and tried to smile, but it was strained.
The conversation apparently over, Donna turned back to the artefacts. She was looking for things she recognised from her parents' memories, but she'd never really paid much attention to that sort of thing.
Harold joined her, and for a while they worked together without speaking. They found several things they could identify, but nothing that might be useful.
Eventually, Harold broke the silence.
"If we opened the Rift… surely we'd be able to close it again?"
"In theory, yes." Now it was Donna's turn to be pedantic, because Harold had phrased it as a question, which meant he wasn't sure he could do it. But she didn't mention it aloud, all the same.
"Only in theory?"
"We'd need Freya, for a start. If she was here - our minds are strong enough. But… do you think we could do it, though? Really?"
And that was the problem.
Harold reached out with his mind, in that newly-discovered way he still didn't understand, finding that indefinable event which would nevertheless define the course of the future.
It was close. Too close for comfort.
After that event, there were two possible ways in which the world could continue. If they managed to stop it, everything continued as normal.
And if they failed, Time would tear itself apart.
How could three children stand against something like that?
"Belief," said Donna sadly. "That's all it takes - belief. But if we don't think we can do it -"
"Then we can't."
The siblings turned back to the alien tech, hoping desperately that they would find something that would be of help, since there was no other way they could undo their mistake.