[ You know, actually? Strange as it is to see a man pull chalk out of his pocket and start talking, it actually helps to see the diagram. As the Doctor explains, Damen's face darkens. He's starting to think about the possibilities.

A world where his father never died.

And world where Laurent's brother never died. What would that world be like? He has imagined it, many times. But that had been a fantasy. He had never imagined that it could be real. ]

You are saying that people could come here from these different worlds. From different versions of my world.

Has that happened before? Or do you think -

[ He pauses, frowning, forcing his mind around it all. ]

- that there is only one world, and we are all from a different version of it?