J. Edgar Hoover grew up in Washington, D.C. with a severe stutter and beat it by teaching himself to talk at ferocious speed. At 18 he took a messenger job at the Library of Congress, where he absorbed a cross-referenced cataloging system and a lesson he never forgot: power belongs to whoever can retrieve and connect information fastest. He carried that method into the Department of Justice in 1917, built paper files on political radicals, and helped orchestrate the Palmer raids. In 1924, at 29, he was handed a scandal-ridden Bureau of Investigation to clean up.

This episode traces 48 years in power across eight presidencies. Hoover turned the bungled Dillinger hunt into a public relations triumph, built a national fingerprint database and forensics lab, and pushed aside the agent who actually got Dillinger. He also denied the Mafia existed until a 1957 mob summit in upstate New York made denial impossible, hid decoded Soviet cables from President Truman, and created COINTELPRO to disrupt groups the courts would not let him prosecute. Presidents complained about him in private and kept him anyway, out of fear and because his surveillance was useful.

• The 1934 ambush at Little Bohemia Lodge in Wisconsin left a civilian shot by mistake and an agent dead while Dillinger slipped out the back windows.
• Hoover locked the Venona decryptions of Soviet spy traffic in his office safe and kept them from his attorney general and from President Truman.
• In 1964 the Bureau sent Martin Luther King Jr. an anonymous package with a tape and a letter that King read as a push toward suicide.
• Richard Nixon admitted on tape in 1971 that he could not fire Hoover because he feared the reprisals.
• Hoover died of a heart attack in 1972 at 77 and became the first civil servant to lie in state in the Capitol Rotunda, while his secretary reportedly destroyed his private records.