The film chronicles the professional life of J. Edgar Hoover, the man credited with founding the modern Federal Bureau of Investigation (FBI). Hoover served as its director from 1924 until his death in 1972, making him one of the most powerful and controversial figures in American history. The narrative delves into the early days of the Bureau under Hoover's leadership, highlighting his efforts to organize and professionalize law enforcement to combat crime across the United States. With a focus on Hoover's methods and innovations, such as the creation of a centralized fingerprint database and forensic laboratories, the film explores his relentless pursuit of notorious criminals. Hoover's drive to protect the nation is depicted against the backdrop of significant historical events, including the fight against communism and the struggle for civil rights.

Parallel to his professional life, the movie depicts Hoover's complex personal relationships, particularly with his close associate Clyde Tolson and his secretary Helen Gandy. Tolson and Gandy are two of the most constant figures in Hoover's life, with Tolson being portrayed as both a colleague and a companion whose relationship with Hoover carries a depth of ambiguity and speculation. Gandy, on the other hand, is a loyal secretary who becomes an invaluable part of Hoover’s professional career, entrusted with secrets that could make or break the powerful director. Their dynamics illustrate the contrast between Hoover's public persona as a staunch, unyielding figure and his private struggles with intimacy, legacy, and power.