Teen computer geek David Lightman innocently taps into the NORAD missile-defense system. This sets in motion what he innocently believes is a war game entitled "Global Thermonuclear War,” but the “game” is the real thing! Nobody can shut down or reprogram the computer that is preparing to launch missiles at the USSR and unleash Armageddon. David and his girlfriend try to aid the helpless Pentagon and, in a race against a quickly ticking doomsday clock, persuades the computer to end the "game."