The first adult history of the F.B.I.- so far as we know- this is done with the full cooperation of J. Edgar Hoover and the organization he heads, and yet is not in the nature of an ""official"" story. It makes absorbingly interesting reading, with its adroit combination of the chronological history, the trial and error methods and inadequacies that marked it through World War I, the development of its present high standard of performance- and the detailed reporting of some of the spectacular cases that the F.B.I. has handled through its years. The text uses as springboard the inexplicable case of mass murder for monetary benefit in the memory of all readers- when Graham dynamited a plane in which his mother was a passenger. This provides a revealing demonstration of how the F.B.I. operates today -- a far cry from the amateurish and often bungling methods when it first came into existence, under Theodore Roosevelt, when he demanded a government agency to investigate fraud in high places. The espionage and sabotage of World War I- the scandals under Harding -- the Red Raids directed by Palmer- all these revealed its weaknesses. Reorganization was begun under Coolidge; J. Edgar Hoover was put at its head- and has stood firmly against vilification and attack through successive administrations since. These years have witnessed the gangsters rise to power, the underworld at its peak, Communism penetrating the body politic and industrial. It has seen also the effective operation of the F.B.I. in breaking the power of the crime leaders, solving some major mysteries and bringing leaders to book, destroying conspiracies, securing legislation, and putting investigation on a high level of trained, scientific procedure. The results have showed themselves in the contrasts between World Wars I and II as regards espionage and sabotage; in the bringing to light of networks of Communistic activities; in stern measures carried through. Postwar crime and attacks on civil rights are under the hatchet- though the end is not in sight. The role of the F.B.I. in loyalty investigations is explored- some of the doubtful factors discussed. And a final chapter clarifies what the F.B.I. is- and what it isn't. This should prove of immense interest to all concerned in factual problems of crime.