Book excerpt: A veteran counterintelligence agent presents a revealing chronicle of his State Department investigations into intelligence leaks and spying on US soil. On October 7th, 1974, Robert D. Booth swore an oath to support and uphold the United States Constitution as a special agent of the State Department’s Office of Security. As a member of the Special Investigations Branch, he investigated numerous information leaks, losses of classified documents, and instances of espionage. Now, in State Department Counterintelligence, Booth reveals some of the most egregious leaks, spies, and lies that have adversely affected national security over his decades-long career. Booth tells the story of his pivotal role in three major counterespionage assignments as well as numerous investigations into unauthorized disclosures—including the unmasking of Fidel Castro’s most damaging US citizen spy. With the narrative style of a political thriller, Booth brings readers inside the real world of counterintelligence.