"You see, everything in the universe is connected in some way or another. What we Timelords did was simply to determine all possible permutations of those links."
Liz looked vaguely sceptical. "And that gave you the power to travel in time?"
"Well, it provided the framework. Rather like your mathematics allows you to progress with the practical side of physics."
"And I suppose it's far beyond the capacity of my limited human brain?"
The Doctor laughed. "For now, Liz, for now. Give it some time."
She sighed. "I wish I could see what you see."
A memory stirred. "It would kill you. A Timelord consciousness in your mind would kill you." He stared at her, red-haired and forthright, and for a moment he saw someone else. A stranger, but familiar. Recognising the feel of his own future, he pushed the thought away. "But...I can give you an idea of what it would be like. Come here."
Liz obeyed, standing a step in front of him, and he reached out both hands to touch her temples. "There," he said softly.
"Oh...." The exclamation fell from her lips. "It's like music."
"Yes. What you can hear is, to use a cliche, the 'music of the spheres'."
Liz stepped back and glanced around the lab. "I'm beginning to understand," she breathed. "It's not seeing...it's more like knowing. Knowing that everything is part of this huge symphony."
"It's a fragile balance," the Doctor said, reaching for her again. "I can't let you perceive it for much longer."
"So this is how you see the universe?" she asked as his fingers brushed her skin. One touch and the feeling was gone, leaving Liz oddly empty.
"Oh no." The Doctor chucked ruefully. "My dear Liz, what you experienced was a mere fraction of a Timelord's mind. No, imagine losing all your senses except taste - that's something of an explanation for what you felt."
She laughed uncertainly and shook her head, hair brushing her shoulders as she did so. "I couldn't live with even that small part."
The Doctor was silent for a moment, reminded yet again of something...someone else he knew he had yet to meet. "Well," he said eventually. "You are only human, after all."
"Oh, there's nothing 'only' about it, Doctor," Liz replied impishly. "Give us a millenium or two and we'll show you."
"I don't doubt it." He paused. "Now, about those tests the Brigadier ordered us to do-"
"Asked. He asked, I made sure of that," she said with a grin.
"I'm sure you did. Anyway, shall we?"
Liz turned on the Bunsen burner. "I don't see why not."