Kevin Flynn is a young and gifted programmer who once worked for the software mega-corporation ENCOM. Flynn created several video games on the ENCOM mainframe while working after hours with the aim of eventually creating his own games company. Before he is ready to present his projects to senior management, his work is stolen by another programmer, Ed Dillinger. Dillinger locks Flynn out of the system and goes on to present the games as his own work, thus earning himself a series of promotions.
Three years later, Dillinger is now a senior executive of ENCOM, and the company is run mainly by the Master Control Program (MCP), an Artificial Intelligence that started as Dillinger's chess program. Flynn, after being fired by Dillinger, has been reduced to running his own video game arcade, which ironically features several of the games he created. As a result, he attempts to break into the ENCOM mainframe and find the evidence he needs to prove Dillinger's wrongdoing. The MCP catches one of Flynn's computer programs, Clu, poking around in sensitive memory and "de-rezzes" (kills) the program. The MCP then summons Dillinger to discuss the matter, and Dillinger authorizes it to shut down access to all personnel in Flynn's former security group. In the process, it inadvertently locks out a current ENCOM employee, Alan Bradley.
Alan goes to speak with Dillinger, and in the process reveals that he is working on a security program named Tron, which would be used to monitor communications between ENCOM and outside systems. When asked, he states that it would not be a part of the MCP, but rather that it would serve as a watchdog for the MCP as well. Dillinger dismisses him quickly, only to be confronted by the MCP about Alan's project. The MCP informs Dillinger that it plans to take over the Pentagon's computer systems, having calculated that it can run things "900 to 1200 times better than any human." When Dillinger attempts to reassert his control over the MCP, it essentially blackmails him into keeping quiet and complying with its wishes.
Meanwhile, Alan goes to speak with his girlfriend, Lora, an ENCOM laser lab technician and Flynn's ex-girlfriend. In the lab, Lora and her coworker have just successfully digitized an orange using a powerful laser (causing it to disappear and reappear intact). Alan and Lora later set off to Flynn's arcade/apartment to warn him that Dillinger knows about his hacking. After being convinced that Flynn is looking for evidence that he was cheated by Dillinger, Alan and Lora sneak him into the laser lab, where he works on forging an access code for a different security group. This would allow him to find the information he is looking for, and would also allow Alan to finish his work and get Tron online.
Flynn settles down at Lora's lab terminal, where her laser points directly at the terminal. As Flynn tries to gain access to the system, he confronts the MCP. While he "chats" with the MCP, it takes control of the laser and suddenly digitizes Flynn into the world inside the computer, where programs are physical characters that resemble their creators.
Flynn materializes in the digital world and is taken to a holding pit. There, a financial program, Ram, tells Flynn that he is a "guest" of the Master Control Program, and that he is going to be made to play games. Flynn, who is convinced that he is dreaming, seems excited about this at first, saying "I play games better than anybody."
Flynn and a number of other Programs are soon taken to meet Sark (Dillinger's counterpart in the digital world). Sark tells each of the Programs that they can either join the MCP willingly, or they will be forced to compete in gladiator-style games that will result in their eventual elimination. Each Program receives an identity disc that stores their actions and experiences, and also doubles as a powerful weapon. On their way back to the holding pen, Flynn sees Tron fighting a number of other Programs, and Ram tells him that Tron fights for the Users.
Before he can return to the holding pit, Flynn is taken to his first game. The game is essentially a vertical version of Jai Alai, except that the players stand on platforms made up of concentric rings that disappear when the ball hits them, forcing them to jump over the gaps. Flynn is forced to face Crom, "one of his own kind" according to Sark. After several volleys, Crom falls off his platform and struggles to climb back up. When Flynn refuses to finish off his opponent, Sark terminates the game and sends Crom plummeting to his death. However, he spares Flynn, recalling the MCP's admonition: "I want him in the games until he dies playing."
Flynn returns to a holding area where Ram and Tron are waiting for him. Flynn immediately mistakes Tron for Alan, and Tron reveals that Alan is his User. Feigning disorientation, Flynn says that he's starting to remember "all sorts of stuff", including that his "User" wants him to take out the MCP. Tron states that that is his goal as well, but before they can talk much more, the three are taken to the Light Cycle arena. In here, the three must attempt to guide their opponents into their trails. They team up and manage to force one of their enemies into the side of the arena, opening a large crack in the wall through which they escape. Sark quickly launches his security forces (which consist of Flynn's Tank and Recognizer programs) to seek them out.
The three locate an I/O tower that Tron needs to access in order to communicate with Alan, but on the way, Flynn's and Ram's Light Cycles are destroyed by a Tank and Tron is separated from the group. Flynn takes the injured Ram to a pile of junk, which turns out to be a damaged Recognizer. He activates it and starts for the I/O tower, but on the way, Ram begins to die. Ram asks Flynn if he is a User, and then he asks Flynn to help Tron just before he dies and de-rezzes.
Meanwhile, Tron breaks into a simulation chamber where a Solar Sailer is being constructed. There, he finds Yori, a program written by Lora. After Tron breaks Yori out of her reporting routine, the two programs make their way to the I/O tower and confront Dumont, the keeper of the tower. He grants Tron access to the port, and Tron receives the critical instructions he needs from Alan in order to destroy the Master Control Program. They then make their way back to the Solar Sailer, narrowly escaping Sark's forces, and set off for the MCP. Along the way, Flynn rejoins them, having accidentally disguised himself as one of Sark's troops. He explains to Tron and Yori at this point that he is actually a User.
Sark eventually captures Flynn and Yori, ramming the Solar Sailer with his ship. Sark then disembarks and begins de-rezzing the ship. Although Yori and the ship begin to fade away around him, Flynn manages to keep her alive and the ship intact. Yori believes Tron to be dead, but in reality, Tron has escaped on Sark's shuttle, which lands nearby the MCP's core. Here, a number of captured programs, including Dumont, are locked against a wall to face the MCP, which appears as a giant red face on a huge spinning cylinder. The MCP senses Tron's presence and sends Sark out to battle him, and then the MCP begins to tell the Programs of their impending fate: "You will each become a part of me, and together, we will be complete."
Sark and Tron battle on the mesa, until Tron gains the upper hand, severely damaging Sark and destroying his disc. The MCP then transfers his functions to Sark, causing him to grow many times Tron's size. Tron begins to attack the MCP directly, attempting to break through the shield protecting its core. As the battle continues, Yori guides the remains of Sark's ship toward the core, where Flynn jumps inside. This distracts the MCP long enough for Tron to throw his disc through a gap in the shield, destroying the MCP.
The digital world comes alive after the MCP's defeat. I/O towers light up all over the landscape, and the Programs rejoice in the fact that their world has become a free system. They ponder Flynn's fate, but Flynn is sent back to the real world, the laser re-materializing him at the terminal. A nearby printer then begins printing the evidence that Flynn's programs were "annexed" by Dillinger.
Dillinger arrives at the office the next morning to discover a message on his computer's screen showing the evidence of his wrongdoing. The movie closes with a brief scene where Alan and Lora greet Flynn at the helicopter pad on top of the ENCOM building. Flynn is now the chief executive of the company.
They actually remade all of the tron games back in 04. I like the new Tron, it's actually a pretty cool game, but I'll never get tired of those old classics. I remember going accross the street from the EQ every day after school to play video games & I'd end up spending all my money on ONE game: Tron.