Presents a fact-based story about the 40 passengers and crewmembers aboard San Francisco-bound flight United 93 on the morning of September 11, 2001. Intercuts mostly real-time scenes of the flight and hijacking with the struggles of air-traffic controllers and U.S. military personnel to comprehend and deal with the unprecedented attacks on the World Trade Center and the Pentagon. Shows how the passengers and crew find out about the tragic attacks through cell phone conversations and unite in a brave attempt to save their lives and prevent their plane from being a fourth weapon in the hands of the terrorists.