J. Edgar Hoover, who took the helm of the Bureau of Investigation in 1924, is regularly credited with the birth of the agency. Yet, the Bureau existed since 1908, provided intelligence, and enforced the neutrality laws for the US government through the tumultuous years of the Mexican Revolution and World War I. It is on the backs of the early federal agents of the Justice Department that the modern FBI emerged. This is the story of these pioneer special agents and their leaders, who on a shoestring budget battled political headwinds and local resistance, to try and prevent the civil war in Mexico from spilling into the homeland.