Computer-game aficionado David Lightman inadverently taps into a hush-hush Pentagon computer, then proceeds to inaugurate his favorite game, "Global Thermonuclear War". David has no clue that the Pentagon, hoping to eliminate the chancy "human element" in the event of an actual war, has given its computer total, irreversable control over the launching of nuclear weaponry. David and government official John McKittrick race against time to reverse the computer's resolve to send bombers to Russia.