The National Security Agency built its post-Cold War empire on intercepting phone calls and emails, and this NOVA episode traces what that machine caught and missed before September 11. Journalist James Bamford, the agency's most persistent outside chronicler, guides interviews with former NSA officials and intelligence analysts who describe a 2000 intercept of calls between hijacker Khalid al-Mihdhar and an al-Qaeda safe house in Yemen, information that never reached the CIA or FBI in time. The film then follows what changed afterward: the NSA's move from foreign-only surveillance into domestic wiretapping without warrants, a program eventually exposed and challenged in court. Former agency insiders describe the technical reach of the eavesdropping systems and the internal arguments over legality that followed. The film sets the successes claimed by NSA defenders against the privacy concerns raised by critics and lets both sides make their case in their own words, without settling the argument for the viewer.