An avid book collector chances upon an auction and buys a lot of assorted books. I think the auction was held in a chateau. The lot of books turns up and, when he goes through them, he finds something rare and special. Upon studying this book things start to happen. The book was, I suppose, a gateway to a higher level of being, something left by those that had gone before as an aid or primer to guide and help the next ones who come along.
As the book is read and studied, things start to happen: people start to die, torn apart, ripped to pieces. People are discovered like this even within rooms locked from the inside. If I remember correctly, it has to do with the darker side of the mind, monsters from the "Id" to quote from that grand old film. The journey to this higher level of being involves leaving behind this dark side. It becomes a residue and those that had gone before had left such a residue; the awakening of this evolution stirs it all up.
Final part of the book talks about how the Earth is silent, no sign of man anywhere, then it talks about an ape finding the book and it ends.