As FBI Deputy Director Miguel Bowman works frantically to address the sudden and mysterious blackout at the Cyber Division headquarters, he issues a critical call to local law enforcement agencies across the nation, urging them to summon the best computer hackers available. NYPD detective John McClane is sent to New Jersey to capture the infamous cybercriminal Matthew Farrell. However, McClane is unaware that this mission will trigger a series of life-threatening events when assassins employed by the formidable hacker and cyber-terrorist leader, Thomas Gabriel, launch a surprise attack on both men during their convergence. In an incredible twist of fate, McClane and Farrell manage to evade the initial ambush, despite the odds stacked against them.
While traveling towards Washington D.C., Farrell reveals that he had been developing an algorithm intended to breach a particular security system for ethical hacking purposes. Meanwhile, Gabriel's team unleashes a catastrophic cyber assault on vital systems, including transportation networks, financial markets, and national infrastructures. Farrell identifies this coordinated strike as a "fire sale," designed to incapacitate the nation’s critical services. As the situation becomes increasingly dire, McClane and Farrell are taken to the DHS headquarters, where they soon find themselves ambushed in a helicopter attack by Mai Linh, who is masquerading as a dispatcher. In a fierce confrontation, McClane valiantly fends off the attackers, ultimately bringing down the helicopter.
After regrouping and planning their next steps, McClane presses Farrell for insights on Gabriel's intentions, eventually leading them to suspect that the cyberterrorist is planning an assault on America’s power grid. Their investigation takes them to a utility superstation in West Virginia, where they discover that Linh's crew has taken control. A ferocious battle ensues; McClane and Farrell successfully eliminate their foes, culminating in a dramatic moment where McClane seals Linh inside a vehicle, which then plummets down an elevator shaft and explodes.
With Farrell preoccupied by the urgent task of mitigating damage from the ongoing threat, he follows Gabriel's digital footprints to upload his image to Bowman. Meanwhile, McClane unearths a troubling revelation about Bowman's past connection with Gabriel in collaboration with the Department of Defense, uncovering a web of intrigue and deceit. Enraged by Linh's death, Gabriel redirects natural gas pipelines leading to the superstation in an attempt to eliminate McClane and Farrell, instigating a catastrophic blackout that threatens the entirety of the Eastern Seaboard.
As the situation intensifies, McClane and Farrell decide to fly to the Baltimore residence of renowned hacker Frederick "Warlock" Kaludis, who uses his expertise to locate a crucial piece of code that Farrell had originally written for Linh. This leads them to a significant data repository at the Social Security Administration in Woodlawn, Maryland, following a trail that ultimately leads Warlock to Gabriel’s hideout, setting the stage for an electrifying confrontation.
In a startling revelation, they find that the seemingly ordinary Woodlawn building is actually an NSA facility designed by Gabriel to safeguard vital personal and financial records in the event of a cyber attack. Seizing the chance when the FBI encounters a blackout, Gabriel attempts to download these sensitive files for his malicious intentions. What’s even more shocking is that he uses the established connection to locate and abduct McClane's estranged daughter, Lucy.
As McClane and Farrell race to the Woodlawn facility, they find themselves in a desperate struggle against time to thwart Gabriel's diabolical plans. While Farrell bravely infiltrates the main server room to encrypt the stolen data, he is captured by Gabriel's henchmen. The cunning terrorist swiftly takes both Farrell and Lucy, leading McClane into a high-stakes game of pursuit and strategy.
Utilizing their mobile command center, McClane commandeers the communication systems of an F-35B Lightning II fighter jet to stay one step ahead of Gabriel's crew. However, when Gabriel instructs the pilot to take out McClane's vehicle, divine intervention occurs in the form of falling debris, which collides with the jet, saving McClane momentarily.
Seizing his chance, McClane bursts into the hangar where Gabriel is hiding, but finds him holding Lucy hostage, with an injured Farrell at his feet. In the escalating tension, Gabriel demands that Farrell decrypt the stolen financial data, but when Farrell refuses, Gabriel callously executes him, placing Lucy's life in grave danger.
Undeterred by his injuries, McClane manages to take down two of Gabriel's henchmen. Despite being shot by Emerson, Gabriel's last loyal supporter, McClane summons his strength to fire a bullet through his own shoulder, fatally wounding Gabriel.
In the aftermath, as the chaos subsides, Farrell manages to recover enough to take down Emerson with a well-aimed shot right as the FBI agents arrive to restore order. McClane, visibly grateful to Farrell for saving Lucy's life, recognizes that their harrowing journey has forged a deep connection between the two men, hinting at the beginning of a new chapter in their relationship.
