A Piece of Blue Sky: Scientology, Dianetics, and L. Ron Hubbard Exposed by Jon Atack.
Its 1990, Kind of old. I have not read it so I can't speak for it.
Here is a link to a document released by the author. It my give you some insight into whether you are willing to spend time and money on his book.
http://www.factnet.org/Scientology/scngen.htmBook Description
Atack exposes Hubbard's bizarre imagination and behavior, tracing the creation of Scientology in the years following World War II to perhaps its final schism following Hubbard's death in 1986. A shocking book that reveals all: the abuses, falsehoods, paranoia, and greed of Hubbard and his pseudo-military Scientologist henchmen.
Also "The Scandal of Scientology" by Paulette Cooper