The story of World War I's volunteer vigilantes--the 300,000 members of the American Protective League who chased phantom spies and saboteurs for nearly three years without catching a single one, but who managed to seriously abridge the civil liberties of numerous loyal Americans. Miss Jensen, who wrote this careful analysis under the guidance of historian Harold Hyman, shows how the League became an amateur FBI (with the support of the Department of Justice and the full knowledge of President Wilson), directing its searches first against enemy aliens, then loyal aliens, dissenters, draft ""slackers"" and labor. The League's existence assumed a German conspiracy to subvert American government, a menace best met by a volunteer counter-conspiracy. Men joined up for a great crusade or to compensate for over-age. Their work ""came nearer to satisfying that pent-up feeling than anything short of going 'over the top'."" For others it cloaked bootlegging and panhandling. APL discipline was poor: serious complaints involved treatment of alien laborers and socialists, but local autonomy impeded investigation. ""Damn the law: we want results,"" a League representative said. Needless to say, after the war the APL was reluctant to disband. For a time members went Red and anarchist hunting, then with the demise of the APL many sleuthed privately for the KKK and the Civil Legion. Able documentation of a chapter in the erosion of civil liberties.