Four fundamentalist Muslim terrorists hijack United Airlines flight 93, headed from New Jersey to San Francisco. Their mission is to take over the plane and fly it into the U.S. Capitol Building, in conjuction with three other hijackings.
The other three hijackings and suicide missions are successful, the planes crashing into both World Trade Center towers and the Pentagon. The passengers aboard United 93 hear the news via cell phone, and realize their flight is also a suicide mission. The passengers hastily arrange an attack and assault the terrorists, killing three of them before the fourth prematurely crashes the plane in a Pennsylvania field.
The caption afterwards notes that there were no fighter defenses between Washington D.C. and United 93, implying that if the passengers hadn't acted when they did, many more innocent lives would have been lost.
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