John O'Neill spent years as the FBI's leading expert on Al Qaeda, tracking Osama bin Laden's network through the 1998 embassy bombings in Kenya and Tanzania and the 2000 attack on the USS Cole, all while clashing with bureau superiors and the State Department who saw him as abrasive and difficult. This FRONTLINE investigation uses interviews with colleagues, friends, and government officials to reconstruct how his warnings about an imminent, large-scale attack on American soil were repeatedly slowed or dismissed by bureaucratic rivalries and turf wars. O'Neill retired from the FBI in August 2001 and took a job as head of security at the World Trade Center. He died there on September 11, weeks after leaving the bureau that had refused to heed him. The film lays out, step by step, the intelligence failures and interagency friction that preceded the attacks, using O'Neill's career as the thread that ties together a broader story of missed warnings inside the American national security establishment.