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 from the counter-intelligence imagination of the FBI. A Threat of the First Magnitude tells the story of the FBI's fake Maoist organization and the informants they used to penetrate the highest levels of the Communist Party USA, the Black Panther Party, the Revolutionary Union and other groups labelled threats to the internal security of the United States in the 1960s and 1970s. As once again the FBI is thrust into the spotlight of US politics, A Threat of a First Magnitude offers a view of the historic inner-workings of the Bureau's counterintelligence operations - from generating "fake news" and the utilization of "sensitive intelligence methods" to the handling of "reliable sources" - that matches or exceeds the sophistication of any contenders.