J. Edgar Hoover, portrayed by Leonardo DiCaprio, is found in his office during his later years, reflecting on a past filled with ambition and turmoil. He invites a writer, played by Ed Westwick, into his office to share the foundational story of the FBI with the public. Hoover reveals that this tale begins in the year 1919 under Attorney General A. Mitchell Palmer, who, amidst political unrest, survives an assassination attempt when a bomb detonates prematurely. This pivotal moment marks the start of Hoover's journey into the realm of criminal science, prompting him to realize the vital need for meticulous crime scene investigation methods.
As his narrative unfolds, Hoover visits his mother, played by Judi Dench, to share that he has been appointed to lead a new anti-radical division by Palmer and is beginning to compile a list of suspected radicals. Shortly after, he meets Helen Gandy, depicted by Naomi Watts, who has just joined the Justice Department as his secretary. During a visit to the Library of Congress, Hoover impresses Gandy with his unique indexing system, but when he tries to kiss her, she rebuffs his advances. Undeterred, Hoover proposes marriage to her, citing her skills and education, but she declines. Nevertheless, Gandy becomes his devoted personal secretary.
In his pursuit of justice against perceived threats, Hoover encounters resistance, particularly from the Department of Labor, which will not act without concrete evidence. However, he exploits the animosity toward renowned anarchist Emma Goldman to orchestrate her discrediting and subsequent deportation, establishing a controversial precedent. Following a series of raids against radical groups, Palmer finds himself out of a job as the political landscape shifts blame for stringent methods. Under new Attorney General Harlan F. Stone, Hoover ascends to director of the Bureau of Investigation, where he soon meets Clyde Tolson, brought to life by Armie Hammer. After recruiting Tolson amidst reviewing applications with Gandy, Hoover strengthens his inner circle.
In present-day revelations, Hoover pressures Robert Kennedy, hinting at blackmail to secure authority over radical factions in exchange for keeping incriminating information about President John Kennedy under wraps. Hoover firmly believes that knowledge equates to power.
By 1932, his Bureau probes into numerous gangster-related crimes, notably focusing on the notorious John Dillinger. When the Lindbergh kidnapping case captures national interest, Hoover implements groundbreaking techniques, such as tracking ransom bill serial numbers and scrutinizing the kidnapper's handwriting. His commitment to crime lab analysis leads to the arrest of Bruno Hauptmann for the crime, and the scientific evidence presented in court ensures a swift guilty verdict, solidifying the FBI's reputation.
As Franklin D. Roosevelt takes office, he questions Hoover's authority, only to be presented with surveillance of his own wife engaging with a known communist. Thus, the President expands Hoover's powers to maintain public discretion. As Hoover seeks further authority from Congress, he faces ridicule for not having made any arrests himself; in retaliation, he begins monitoring dissenting congress members, discarding agents who seek popularity.
On a personal note, Hoover and Tolson's relationship deepens amidst societal expectations when Hoover expresses reluctance to dance at a social event. This friction leads to a confrontation between the two, culminating in a passionate altercation that reflects their complex bond. As their relationship evolves, Hoover ultimately admits his feelings for Tolson, resulting in temporary resolution.
Years later, as Hoover confronts his declining health and impending mortality, he grapples with the legacies he crafted. His attempts to tarnish Martin Luther King, Jr.'s reputation falter as King accepts the Nobel Peace Prize. Meanwhile, Hoover instructs Gandy to destroy his secret files upon his death to protect them from future scrutiny. As Tolson urges Hoover to retire, Hoover remains steadfast, anxious about the future of the Bureau he has painstakingly built.
Upon Hoover's passing, Helen Gandy is depicted destroying volumes of files, presumably his controversial "personal and confidential" documents, while a televised eulogy from Nixon unfolds, encapsulating the complex and often tumultuous story of one of America's most notorious figures.
