On a beautiful May morning at JFK Airport, a routine plane departs for San Francisco. Security agent Bernice Adams finds a postcard of the Golden Gate Bridge bearing an ambiguous message. Who left the postcard behind, which flight is that person on, and what exactly does the message mean? Her supervisor dismisses her concerns but she is compelled to contact Homeland Security. Someone's planning something terrible and these passengers' lives entwine as they come together to help to avert a tragedy at the eleventh hour.