"The Nature of Universes" was a book written by Doreen Austerlitz.
Lust from Beyond (Spoilers)
After he is captured by the Scarlet Lodge, Victor is sent by Dr. Austerlitz to retrieve the book from Lusst'ghaa and "return [it] to the Austerlitz family." Victor succeeds, much to the Doctor's delight.
In the book, Doreen claims that the information contained within is "based on the interrogations of a dozen Seeing Ones." If this is true, and Doreen had indeed met that many Seeing, then it raises several questions. She claimed to have created the Cult of Ecstasy in order to locate a child of Seeing to sacrifice and bring about the conjuction of our world and Lusst'ghaa. Did none of the twelve questioned for the book have children? Or did Doreen hide them from the Cult for some reason?