The publisher is trumpeting how Kessler's revelations here of William Sessions's abuses of office led to the former FBI director's dismissal—but those revelations form only one small part of Kessler's comprehensive, largely approving examination of how today's FBI emerged from the shadow of J. Edgar Hoover. Sessions granted former Wall Street Journal and Washington Post reporter Kessler (Escape From the CIA, 1991, etc.) unprecedented access to the agency, which Kessler used to gain more than 300 interviews. In the process, while picturing Sessions as a generally decent man who made a point of hiring women and minority agents, Kessler also found him to be an agency cheerleader who disguised personal travel as business trips and turned a blind eye to similar exploitation of power by his wife and assistant. But despite its chiefs' failings (according to Kessler, all but William Webster took improper advantage of their position), today's FBI, Kessler says, is ``an American success story'' that, unlike the publicity-minded institution of the Hoover era, is willing to zero- in on large targets that may not yield immediate results, such as drugs, white-collar crime, the Mafia, and political corruption. Though occasionally embarrassed—recent years have seen racial- discrimination suits; requests that librarians identify users of scientific and technical information; the first agents caught trading secrets to the Soviets, dealing drugs, and attending a sex club—the FBI retains its cadre of dedicated, well-trained agents. Elegant prose isn't Kessler's strongest suit (he repeatedly describes women as ``attractive'' or some variation thereof), but he's gotten agents to open up about the organization's inner workings. Field offices such as L.A. (which combats auto theft, drug-dealing, and celebrity-stalking) and N.Y.C. (which cracked the World Trade Center bombing) are described, as are the famed training and serial-killer ``profiling'' divisions, featured in The Silence of the Lambs. A revealing glimpse of an American institution in transition. (Photographs)