When a test performed by the North American Aerospace Defense Command (NORAD) Combat Operations Center reveals that 22% of missile commanders do not fire weapons despite a direct presidential order, John McKittrick, the officer in charge of computer operations, suggests that men be taken out of the loop altogether and replaced with a computer. The computer he recommends, the War Operation Plan Response, or WOPR, would have the sole task of calculating every possible scenario through playing war games. He suggests the computer could respond in a more efficient manner than humans. A presidential aide agrees and counsels the President to implement the WOPR system. Meanwhile, in Seattle, Washington, teenager David Lightman plays the video game Galaga at a local arcade before rushing off to school. He arrives late to his Biology class, discovers that he has failed a test, and is sent to the principal's office for making wisecracks. While waiting for the principal, David makes a mental note of the password to the school computer that is written on a piece of paper in the pull out panel of a desk. After school, David gets a ride home with his classmate, Jennifer Mack. She observes that they have both failed their Biology exams and that they will be in summer school together. David says that he will not have to go, and when Jennifer asks why, he shows her to his room. He calls the school from his phone, connects to its computer by typing in the password, and changes their Biology grades to C’s. Jennifer demands that he change hers back, but after she leaves, he gives her an A. Later, David looks at a Protovision advertisement for a new computer game. Wanting to play the game before it is released, he attempts to hack Protovision’s mainframe by programming his computer to dial up all computers in the area code where the game company is located. The following day, Jennifer meets David at the arcade to ask for her grade to be changed. When she returns to his room, she notices David’s computer scanning numbers and once it finishes, David looks through the list of computers, trying to access Protovision. However, one computer does not identify itself and promptly kicks him off the connection. Curious, he tries again, this time typing “Help Games.” The computer lists several normal games, such as chess and checkers then lists war simulations, such as Global Thermonuclear War. Realizing that the system he accessed is not Protovision, David shows a printout of the games to his friends at a high-tech computer facility, and they recognize it as a military system. They declare it not hackable, but David researches the system’s creator to find a possible “backdoor” secret password, and discovers a man named Falken, who invented a game to teach computers not only how to think, but to learn from their mistakes. David also finds that Falken's son, Joshua, was killed in a car accident with his mother, and that Falken died soon after at the age of 41. Hit by sudden inspiration after Jennifer comments on the tragedy of Falken’s life, David tries “Joshua” as the computer login password. The computer accepts the prompt, responding “Greetings, Professor Falken.” Ecstatic, David switches on a human voice computer signal interpreter and converses with the computer, which eventually asks if he wants to play a game. David responds that he wants to play Global Thermonuclear War and the computer hesitantly accepts. When prompted to pick sides, David chooses to be Russia and sets his primary targets as Las Vegas and Seattle. Meanwhile, at the NORAD Command Center, the system picks up incoming Russian missiles targeted at Las Vegas and Seattle. As David and Jennifer have fun with their game, the military prepares for nuclear war. While tensions mount at NORAD and the president is called for executive orders, David gets in trouble with his parents for not fastening the lids on the trash bins and has to shut his computer down to clean up the resulting mess. All missile threats at NORAD vanish, leaving General Beringer to realize that someone has hacked WOPR, and they track the offending computer to Seattle. When David sees a news bulletin on television reporting that the U.S. military thought the Russians had launched a surprise attack and blame a computer malfunction, he realizes that he almost initiated World War III and throws away his research on Falken. WOPR, however, calls David, who it thinks is Professor Falken, and insists on continuing to play the game until it is won, enabling the FBI to track him down. After taking him to NORAD, officials meet to determine the validity of David’s story and whether he might be a Soviet spy. David is introduced to McKittrick, who worked with Falken. David reiterates that he just wanted to play a game, that WOPR called him back and that it is still playing Global Thermonuclear War. McKittrick is called away from his meeting with David to learn that WOPR’s missile launch codes have been stolen and assumes that David is working with outside forces, and General Beringer orders the defense readiness status to be increased to DEFCON 3. While McKittrick is out of his office, David logs into McKittrick’s computer with the password “Joshua” and learns that Falken is alive but living under a new identity as Dr. Robert Hume. He discovers Falken’s classified address is on Goose Island in Oregon. As David is dragged from the office, he yells to McKittrick that Joshua will to try and win the war at any cost, and begs him to call Falken. David is locked in the infirmary, but breaks out by overriding the security code. Crawling through air ducts and blending in with a group of tourists, David sneaks off the base. He calls Jennifer, asking her to buy him a plane ticket for him to Oregon. Jennifer meets him at the airport, and they head to Falken's island retreat. Meanwhile, at NORAD, the perceived threat of a Soviet attack heightens and General Beringer, who sees the Russian’s denial of the operation as a bluff, increases the alert status to DEFCON 2. Two air force pilots are deployed but report back that they do not pick up Russian aircraft on their radars. Back at Goose Island, Falken explains his belief that humanity is destined to destroy itself, and therefore refuses to help. He says that the failure in his programming of WOPR, as well as with government officials in the War Room, is that they are unable to realize that some games, such as tic-tac-toe and nuclear war, are unwinnable. David and Jennifer try to reason with him, but he remains unmoved. The pair tries to leave the island, only to find there is no boat. Regretting the lost opportunities in their lives that will be cut short by nuclear war, they kiss. A helicopter appears with Falken in the cockpit. He motions them to get in, and they fly to NORAD headquarters where tension continues to mount and the status is changed to DEFCON 1, World War III. Just as the security doors are sealed, Falken, David and Jennifer slip into NORAD and discover that WOPR is simulating over 300 nuclear missiles, a fleet of nuclear submarines, and an army, all focused on attacking America, and the president is about to give the command for a counter-attack. Falken explains to General Beringer that the threat is only a simulation and that the entire sequence is a bluff by WOPR in an attempt to provoke an American attack on the Soviet Union. Falken begs the general to question the logic of why the enemy would attack without being provoked and to understand that he is listening to a machine and should not act like a machine, himself. Convinced, the general decides to ride out the attack. He calls commanding officers from several prime targets and tells them to stay on the line as long as they can. The entire command center watches as the bombs on the screen explode, apparently obliterating their targets. After a few tense seconds, the commanding officers at the presumed targets announce that they are still on the line. Realizing the bombs really were a simulation, the command room explodes with joy. However, Falken soon notices that WOPR has locked the system and is attempting to calculate launch codes to “retaliate” against the Soviet Union, testing every possible sequence of numbers and letters on the main control screen. When Jennifer tells David that he never should have started playing games with the computer, he is struck with the idea to ask WOPR to list games, just as he had done initially to break into the system. WOPR responds, but continues to test the code, having already determined three of the ten digits. When the list of games comes up, David tells the computer to play against itself at tic-tac-toe. He explains to General Beringer that WOPR must learn that some games cannot be won. Just as WOPR solves the launch code, it realizes that tic-tac-toe is unwinnable and then applies that knowledge to Global Thermonuclear War. The missiles start running their launch sequence, but as the WOPR tries to solve the losing game, it pulls power from every other system in the command center, causing a total blackout. After a few moments, the main screen comes back on. WOPR addresses Falken, commenting that Global Thermonuclear War is “a strange game. The only winning move is not to play” and asks to play a game of chess instead. General Beringer orders the status of the defense alert system be returned to its lowest state of readiness, DEFCON 5.