"Long story." Donna looks about for a bench and sits down. She sighs, "The Library - it was a planet. But it was infested by these tiny creatures called the Vashta Nerrada. The Doctor and I were summons there by River on his Psychic Paper, but she had intended it to get to him in the future.... anyway. The Doctor felt it was getting to dangerous for me, so he sent me back to the TARDIS via teleport but it went horribly wrong. The Library Computer system... downloaded me, for lack of a better phrase. And a great big alternate universe popped up around me."