In 1989, seven years after defeating the Master Control Program, Kevin Flynn (Jeff Bridges), the innovative software engineer and the CEO of ENCOM International, disappears. Twenty years later, his son, Sam (Garrett Hedlund), who became ENCOM's controlling shareholder after his father's disappearance, takes little interest in the company besides an annual practical joke on the board of directors. Sam is visited by his father's friend and ENCOM executive Alan Bradley (Bruce Boxleitner), who urges Sam to investigate a mysterious page originating from Flynn's old arcade, which was disconnected for twenty years. While exploring the shuttered arcade, Sam discovers a concealed computer laboratory and unintentionally transports himself to the Grid, a virtual world inside the computer.
Sam is captured and taken to the game arena, where he is pitted against Rinzler, the champion of the games. During their duel, Rinzler notices that Sam is not a Program but rather a User. Rinzler takes Sam before CLU, a digital copy of Kevin Flynn, who rules over the Grid. CLU nearly kills Sam in a Light Cycle match before Quorra (Olivia Wilde) rescues him. Taken to a distant, off-grid hideout in the "Outlands," Sam is reunited with his father.