The untold story of the FBI informants who penetrated the upper reaches of organizations such as the Communist Party, USA, the Black Panther Party, the Revolutionary Union and other groups labeled threats to the internal security of the United States.

Sometime in the late fall/early winter of 1962, a document began circulating among members of the Communist Party USA based in the Chicago area, titled "Whither the Party of Lenin." It was signed "The Ad Hoc Committee for Scientific Socialist Line." This was not the work of factionally inclined CP comrades, but rather something springing...