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.htm
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