Dallas, Texas. 1983. Joe MacMillan meets Cameron Howe while speaking at a university. They have sex in the back room of a bar.

At Cardiff Electric, a system software company, SVP John Bosworth hires Joe for a sales position, impressed by Joe’s stellar sales record at IBM.

Joe asks Gordon Clark, a sales engineer at Cardiff, to help him secretly reverse-engineer an IBM PC. Gordon’s wife, Donna, warns Gordon against the proposition, given that their last failed computer venture — the Symphonic — drained their finances. Gordon helps Joe anyway and recreates the assembly language code for an IBM BIOS chip.

After Joe alerts IBM to his endeavor, IBM threatens to sue Cardiff Electric for copyright infringement. Nathan Cardiff, owner of Cardiff Electric, begrudgingly lets Joe and Gordon proceed. In order to avoid copyright issues they hire Cameron — a software engineer who doesn’t know Cardiff Electric or IBM — to replicate the BIOS chip on her own.

Joe unveils his vision to Gordon and Cameron: creating a PC that is two times faster than IBM PCs but half the price. As Cameron starts working on the BIOS, she routinely hits up Joe for sex as a way to clear her mind.

As retribution, IBM poaches 15 of Cardiff Electric’s accounts, causing Cardiff to lose 68% of its billings. Gordon is forced to fire 46 employees.

IBM’s SVP visits Joe on behalf of Joe’s father, an IBM honcho, and invites Joe to return to IBM — even though Joe destroyed an IBM data center at the end of his time there, incurring $2 million in damage. Joe refuses. Meanwhile, Cameron is approached by IBM with an enticing job offer but she turns it down.

Joe modifies his PC vision and tasks the team with building a portable computer that weighs less than 15 pounds and has two floppy drives, an integrated screen and keyboard. Brian Baswell, Gordon’s colleague and neighbor, tells Gordon it’s impossible. Tired of Brian’s negativity, Gordon fires him. Meanwhile, Donna devises an ingenious solution to increase the PC’s speed with a negligible increase in size.

Nathan Cardiff arranges a meeting with local heiress LouLu Lutherford, a potential investor for the PC program. Bosworth agrees to LouLu’s offer to buy 80% of the PC project for a paltry $10 million. Joe intentionally sabotages the deal by making out with LouLu’s trophy husband then proposes an alternate plan: reduce the production timeline to three months, build a prototype on their own dime and then unveil the PC at COMDEX, the annual industry expo.

The PC team bubbles with excitement as Cameron’s code nears the Doherty Threshold, which means the PC will have a nearly instantaneous response time. A Wall Street Quarterly reporter arrives at Cardiff Electric just as Cameron discovers that her code was erased — seemingly by a power surge triggered by the janitor’s vacuum cleaner. As panic ensues, Gordon brings in Donna to retrieve the data. Donna later realizes that Joe orchestrated the BIOS crash for publicity and privately confronts him.

As Donna helps Gordon with the Giant and also picks up the slack in parenting, her work performance at Texas Instruments lags. She’s scolded by Hunt Whitmarsh, her boss and childhood friend.

Once Cameron finishes the BIOS code, Joe hires a new team to program the software. Cameron bonds with her new cubicle-mates, Lev and Yo-Yo.

Gordon proposes an LCD screen to reduce the PC’s weight. He convinces his father-in-law, Gary, to arrange a meeting with his client, Kuzoku, which manufactures LCD screens. Joe strikes a deal with Kuzoku but Gordon ruins it when he drunkenly badmouths Gary to the horrified Kuzoku executives. Gary salvages the deal after Gordon begs him for help.

Joe agrees to meet his father, who is visiting town, but stands him up at the last minute. Joe Sr. runs into Cameron at Joe’s apartment and criticizes Joe. “It’s only a matter of time before he blows everything up. He always does,” he predicts.

The PC team cheers as they power up the prototype for the first time. Cameron fires the software manager that Joe hired and takes over the programming team. She then proposes an operating system that interacts with users — a way to give the PC “a soul.” Joe greenlights the idea despite objections from Gordon, who says the new OS would slow the PC down. In a fit of anger, Gordon lets slip to the programmers that Cameron is sleeping with Joe.

Donna tells Hunt about Gordon’s project. He praises Donna’s Texas Instruments reports and invites her on a business trip to present her findings.

Gordon invites Joe to dinner with the intention of convincing him to drop Cameron’s OS. When Gordon shows up late to dinner, Donna argues on his behalf.

Bosworth learns that the PC division is operating at a deficit and will bring down the company within days.

Joe hires a prestigious industrial designer, Simon Church, to design the PC’s case, but Gordon chases him off. Simon, who is also Joe’s former lover, agrees to come back and design the case. He warns Cameron that Joe will eventually get bored with her.

Donna accompanies Hunt on a business trip and impresses TI executives. She kisses Hunt at the hotel but he pulls back. Mortified, she returns home early only to find Gordon maniacally digging an enormous hole in the backyard. He is looking for a giant from a bedtime story.

The FBI raids Cardiff Electric and arrests Bosworth for hacking. Cameron admits to Joe and Gordon that she helped Bosworth hack into Nathan Cardiff’s bank account to steal money for the PC division, which he planned to repay after COMDEX.

Gordon hides the PC prototype — which they’ve named the Giant — before the FBI can take it as evidence. He brings the prototype home and excitedly invites Donna to join them at COMDEX. Fed up with Gordon, Donna decides to leave him but changes her mind when she turns on the Giant. She smiles at the OS’s personality.

Hunt resigns from Texas Instruments.

Joe tries to secure an early order for the Giant but is told by his business associate that IBM is rumored to be debuting its own portable PC. He flies to New York to confront Joe Sr., who confirms the rumor. In a show of defeat, Joe accepts his father’s offer to return to IBM on the condition that he oversees the portable PC division. Back in Texas, however, Gordon convinces Joe to stay with Cardiff, saying the FBI scandal will drum up attention at COMDEX.

At COMDEX, the Cardiff team loses their suite and premium booth space due to frozen funds from the FBI investigation. Gordon finagles a suite while Donna secures a small booth in a remote corner of the floor. Cameron lures attendees to the booth by building an enigmatic display. Joe later drums up excitement for the Giant by throwing a big party in the suite.

As Joe and Gordon prepare to unveil the Giant, they see Hunt and Brian promoting their own PC, the Slingshot, at a nearby booth — a blatant Giant rip-off that is faster and cheaper. As the team panics, Donna admits to Gordon that she kissed Hunt.

Gordon removes Cameron’s OS to make the Giant faster and cheaper than the Slingshot. Cameron pleads with Joe to put the OS back but Joe takes Gordon’s side. After Joe delivers a successful demo, they sell 60,000 units on the spot, defeating the Slingshot. Later that night, the team glumly celebrates without Cameron. Joe visits the Apple suite and watches the crowd gasp and applaud as a Macintosh boots up. “It speaks,” he says in quiet awe.

Joe and Gordon convince Nathan to cede them each a percentage of the company and joint operational control after they net Cardiff $40 million. As the team tests the first shipment of Cardiff Giants, Joe wishes the Giant had been more innovative. He enlists the programmers to design a “killer app” to bundle with the computer but is not impressed by their uninspired ideas. Joe begs Cameron to return to Cardiff Electric but she refuses, calling him “a sad little boy with a lot of wasted potential.”

Cameron takes a job with a phone company and engineers a technology that uses phone networks to move data at high speeds. She then quits and starts her own company, Mutiny, which allows users to play games with each other via dial-up modems. She poaches all the Cardiff programmers and hires Donna, who has quit Texas Instruments, as her hardware engineer.

After the Giant launch party, a demoralized Joe torches the first shipment of Giants and disappears from Cardiff. Weeks later he walks off into the wilderness.