While trying to hack into a video game software company, high school prodigy David, portrayed by Matthew Broderick, accidentally makes a wrong turn and connects to a top-secret Pentagon computer instead, which has been programmed to eliminate human error and emotions, and has complete control over the United States’ entire nuclear arsenal. The computer has been trained to make certain decisions by implementing different game simulations. What David and his friend Jennifer, played by Ally Sheedy, think is just a new video game called Global Thermonuclear War is actually driving the computer to make tactical decisions in real life. Based on player moves in the game, the computer is prepared to launch bombers to the Soviet Union. Once David realizes his gaming could potentially start huge problems between major countries, he eventually teaches the computer through several tied games of tic-tac-toe that some games cannot be won, and the computer learns that the use of nuclear weaponry will not lead to any player winning, shutting down its launch plan.