Tim Weiner's "Enemies" and F.B.I. Counterintelligence F.B.I. Director J. Edgar Hoover, left, and Associate Director Clyde Tolson at a 1950 hearing about Dr. Klaus Fuchs, a British scientist accused of giving top atomic secrets to Russia. First things first: Tim Weiner's new book, "Enemies: A History of the F.B.I.," is an outstanding piece of work, even-handed, exhaustively researched, smoothly written and thematically timely. What it is not is a history of the F.B.I. Here's the thing: For 104 years now the Federal Bureau of Investigation has essentially worn two hats - its traditional law enforcement "arrest a bad guy" hat and its more controversial intelligence hat. The latter is the part of the F.B.I. that from World War I on investigated all manner of political radicals and Communists, compiled lists of Americans to be detained in the event of national emergency and engaged in at least half a century of illegal wiretapping, mail opening and burglaries. It's this side of the shop - and exclusively this side - that interests Mr. Weiner, a former reporter for The New York Times. This shouldn't be too surprising, given that Mr. Weiner previously wrote an admired history of the C.I.A., "Legacy of Ashes." So, in a 500-page book on the F.B.I., this means not a word on Louis Buchalter - no Mafia at all in fact. There are only glancing references to Waco and Ruby Ridge, and barely a single sentence on the bureau's Depression-era scramble to hunt down the likes of John Dillinger and Pretty Boy Floyd. This is like writing a history of the New York Yankees but ignoring Whitey Ford and the other pitchers. That said, what Mr. Weiner does, he does very, very well. This is certainly the most complete book we are likely to see about the F.B.I."s intelligence-gathering operations, from Emma Goldman to Osama bin Laden. The problem with some F.B.I. histories is that they come off as a list of unrelated cases - case after case after very old case. Where Mr. Weiner excels is in connecting the dots. He identifies his themes, almost all involving the conflicting demands of civil liberties and civil order - "the saga of our struggle to be both safe and free," as he puts it - and rigorously pursues them. As far back as 1941, for example, he finds echoes of the contemporary debate over military tribunals in the F.B.I. case against a group of Nazi saboteurs who, after a peremptory trial before a secret court approved by President Franklin D. Roosevelt, were executed within weeks of their arrests. Illegal wiretaps and burglaries were the F.B.I."s key weapons almost from the beginning. Time and again, going back to the 1930s, this or that court would rule such procedures illegal. Time and again, J. Edgar Hoover, the bureau's director from 1924 until his death in 1972, simply ignored the law. A string of presidents, from Roosevelt to Richard M. Nixon, knew exactly what the bureau was doing and refused to stop it. "Despite (their illegality)," the assistant director William C. Sullivan wrote in a memo to Hoover in the early 1960s, "black bag jobs have been used because they represent an invaluable technique in combating subversive activities of a clandestine nature aimed at undermining and destroying our nation." Illegal activities were so ingrained that Hoover himself, after an embarrassing court disclosure in 1966, ordered them stopped and was ignored. Even after his death, after still more court orders against wiretapping and black bag jobs, Hoover's successors continued to defy the courts, in acts that eventually got one F.B.I. director, L. Patrick Gray, indicted, and the bureau's No. 2 and 3 men convicted. In time the bureau's top men simply didn't know how to run an investigation without breaking the law. Another weakness of some F.B.I. books is their portrayal of Hoover as either a Machiavellian villain or, worse, a figure of unassailable power. He was neither. Mr. Weiner does a superb job, maybe the best I've seen, at charting the ebbs and flows of Hoover's power, chronicling in detail his relationship with presidents over 40 years. For each, Hoover wooed the new president by opening his dossier of gossipy secrets, and almost to a man, the president was immediately hooked. Only Harry S. Truman, and to a lesser extent John F. Kennedy, consistently resisted Hoover's charms; just about every time Truman mentioned the F.B.I., he managed to use the word "Gestapo." And only Nixon made any serious effort to replace Hoover, after the director, near the end of his life, wouldn't go along with committing crimes far worse than his own. Bryan Burrough, a special correspondent at Vanity Fair, is the author of "Public Enemies: America's Greatest Crime Wave and the Birth of the F.B.I., 1933-34" and "The Big Rich: The Rise and Fall of the Greatest Texas Oil Fortunes."