This was a great read until almost the final page. The author takes the reader back through the life of this American icon and collates facts which, until recently, were either unknown or simply gossipped about in the odd documentary or article: Hoover as, almost certainly, a transvestite gay, who lived with a long term companion (officially an FBI officer on the payroll) and as a chief of secret police (by any other name) whose main stock in trade was collecting the dirt on possible threats to his position. This latter is certainly a trait of all top secret police people (examples might include Beria, Himmler and Bormann, the last not exactly a secret policeman but a hybrid).
The book goes through Hoover's career and makes the point that he did not, contrary to popular belief, found the F.B.I. at all, that he investigated those whose arrest would make good publicity, that he neglected to chase those criminals who were in the background, like the Mafia (whose chiefs had plenty of information about Hoover's own peccadilloes) etc. There are also interesting bits about the Kennedy assassination and about the WW2 spy Popov (see his own book Spy Counter Spy).
I thought the book very good indeed, weakened really only by the very end, where an attempt is made to diagnose Hoover retrospectively via various experts in psychiatric disorders. That weakened the book, not least because the conclusion, typical of psychiatry (?) is that Hoover was a paranoiac, also a sociopath, also a sexual deviant, etc...no real conclusion.
Well worth reading and a salutary lesson in the old tale of how power corrupts, though the author does make the point (not very strongly, though) that the organization Hoover created did and does have strong suits, particularly in the technical aspects of its work. The F.B.I. has had many many successes to place against its failures.