On Christmas Eve 1987, John McClane sits on a flight headed towards Los Angeles, CA. A fellow passenger notices he is stressed about the flight and recommends that he take the time to make barefoot fists with his toes on carpet after he arrives to his destination as a cure for jet lag. After landing and collecting his luggage, John sees a chauffeur holding a sign labeled "J. McClane". The driver, Argyle drives him to Nakatomi Plaza and on the way roots out that John still works as a police detective in New York City but that his wife, Holly Gennero, relocated to California for a great career. Both John and Holly thought the other would bend and move to join the other, but that they are both too hard headed.
Meanwhile, at Nakatomi Plaza Joe Takagi addresses the employees of the Nakatomi Corporation at their company Christmas party in the Floor 30 foyer. He announces that that day was one of the most successful days in the company's history. Holly Gennero walks through the crowd, finishing up some paperwork. As she walks down a hallway, her co-worker Harry Ellis flirts with her. When she arrives at her office, she excuses her pregnant secretary Ginny to go join the party and shows Harry the door as well. She then speaks with her young daughter Lucy and nanny Paulina on the phone about John's arrival, stating that she isn't certain if he made his flight or not. She looks at a photo of her, John, and their children; Lucy and John, She sighs and places it face down on the shelf.
John's limo pulls up to the entry of Nakatomi Plaza. Argyle tells him he will wait in the garage until John calls and informs him that he's made other plans. John greets the security guard and uses a computer to find out that Holly has changed her last name to her maiden name, Gennero. He takes the elevator to the 30th floor, walks through the party and meets Joe Takagi who shows him to Holly's office. In the office sits Harry Ellis, who obviously finished snorting cocaine moments earlier. He introduces himself and John informs him that he "missed some", and Harry quickly brushes his nose with his fingers. Holly enters, and the two jilted lovers give each other a subtle greeting across the room. Harry informs John that Holly just closed the biggest deal in the company's history and received a new Rolex watch. Joe and Harry leave as John asks for a place to wash up. As John washes up, the two comment that the missed each other but quickly begin arguing about Holly's decision to move to California. They are interrupted by Ginny who requests Holly join the party.
A Mercedes pulls up to the Nakatomi Plaza entry as a courier truck pulls into the garage. Theo and Karl approach the Nakatomi Security Guard 1 at his desk while Theo talks about basketball nonchalantly, and Karl shoots the guard in the forehead. Theo hops over the desk and begins using a computer to shut off all the elevators in the building except one, as well as sealing all the exists to the garage and the building. Karl uses a flash grenade and his silent pistol to take out the other security guard. In the garage, Hans Gruber and the rest of the team of terrorists exit from the back of the courier truck. Hans seals the front door while Eddie puts on the guard's jacket and mans the desk. Tony makes his way to the telephone junction boxes and begins patching in to the system. He barely finishes patching in before his brother Karl uses a chain saw to cut through all the phone cords to prevent any calls from leaving the building.
Meanwhile, a barefoot John is making fists with his toes and is surprised it is working to cure his jetlag. He calls Argyle but is cut off (by Karl's cutting of the phone lines). Hans and some of his henchmen arrive via elevator to the Christmas party and begin fairing at the ceiling to capture everyone's attention. John hears the gunshots and is able to sneak out of the office into the stairwell with his police-issued handgun. He nearly enters the 35th floor, but notices other henchmen wheeling equipment through the hallway. He continues up to Floor 32 which is under construction, where he tries to gather his thoughts and think of a way to alert authorities.
In the foyer, Hans informs the Nakatomi Corporation employees that he is going to teach the company a lesson on "the real use of power" because their company has "a legacy of greed". He calls out for Joe Takagi, but Holly tells Joe to stand back. He steps forward after Hans lists several detailed facts about his life. Hans greets him and the two take the elevator to Floor 34. In the board room, Theo asks Takagi for the CEO daily key code and encryption number. Takagi insists that he doesn't have them, and even if he did they couldn't steal any information that would hurt the company. Hans corrects him that they aren't after information, but the $640 Million in bearer bonds in the company's vault. John McClane enters from the stairwell and overhears the interrogation of Takagi. Hans gives Takagi to the count of three to give him the codes, but he refuses. Hans shoots him in the head, orders Tony to dispose of the body and Theo to begin hacking into the vault. John makes a noise as he escapes from the room, but the terrorists don't find him and dismiss the noise. In the garage, Argyle listens to loud music in the limo, talking to a girl on the phone.
Heinrich, Marco, and Uli work in a room full of the building's heating and cooling machinery. They wire the room with what appears to be explosives. Theo and Hans walk to the vault while Theo explains the vault's seven layers of security. He stresses that he can complete the first six, but that the seventh lock, a electromagnetic system, can not be cut locally. Hans guarantees he has a plan. John curses at himself on Floor 32 and suddenly comes up with a plan: pull the fire alarm. Eddie informs Hans of the alarm, and Hans orders him to call 911 to disable the alarm and turn off the system. John celebrates the approaching fire trucks but gets angry when they turn off their sirens and turn around. Tony enters the room and John hides. He searches for John in the labyrinth of the construction. The fight, crashing through drywall and aluminum beams and stumble down a stairwell. Tony dies in the fall.
In the vault, Theo bypasses the first level of security and begins using a drill to proceed the heist. John takes Tony's radio, lighter, and Heckler & Koch MP5 machine gun. He then dresses up Tony's body on a chair in the elevator and sends it down to the Christmas party. Hans frightens the party by telling them that Mr. Takagi has been killed, but is interrupted by the arrival of Tony's body. He is angered by the message on Tony's sweatshirt: "Now I have a machine gun. Ho-ho-ho." Riding on top of the elevator, John listens to the terrorists and takes notes on his arm. He rides the elevator to the top floor and sneaks out to the roof.
Meanwhile, Hans tells Karl that Tony, which enrages Karl and that he wants vengeance. Hans tells him that he'll get it, but after Heinrich and Theo finished their jobs.
McClane arrives at the roof and uses the CV radio to call out on frequency 9, but is chided by the 911 operator. He yells at her to send help, but Karl and others begin shooting at him, prompting him to evade. The operator decides to send a sole officer to investigate. Al Powell receives the call while buying Twinkies for his pregnant wife.
On the roof, John evades the gunfire and makes his way into a dead-end closet with a large ventilation fan. He blocks the fan with his gun, climbs through, and evades the terrorists back to Floor 35. Still pursued, he is cornered in the elevator shaft and must climb down the ventilation shaft to Floor 34. He uses his machine gun and it's strap to climb down the ventilation shaft, but the strap slips free from the gun and he falls a couple of floors. He manages to catch himself on a ledge and climb into a horizontal vent. He uses the lighter to see in the vent, but Karl sees the light and follows him to Floor 31. Karl shoots at the ducts and begins pressing them, checking for body weight, but is called away before he finds John.
McClane exits the shaft and watches as Al enters the building and is fooled by Eddie disguised as a security guard. John attempts to break the window with a chair but is spotted from the roof by James. He radios Marco and Heinrich and they ran to stop him. Marco appears to surrender, but John shoots Heinrich when he runs in. Marco then traps John under the conference table by standing on top and shooting toward the ground. At the end of the table, John reloads his weapon and shoots Marco through the table, killing him. He sees Al leaving the building, and throws Marco's body on his car to alert him that there is trouble. The terrorists open fire on Al's car and he calls for backup and manages to drive in reverse over a retaining wall. He is jostled, but is able to walk out of the car. In a news equipment room, journalist Richard Thornburg overhears the call for help on a police scanner. He argues with a news producer and insults a news host seconds before he goes on the air, and is given a truck to investigate the story.
As police arrive at Nakatomi Plaza, John harasses Hans over the radio. Hans insults him for watching too many cowboy shows on TV, but John takes it as a compliment, insisting he likes Roy Rodgers. He then signs off by saying "Yippie-ki-yay, motherfucker!". Hans gets a status report from his men, and learns that Theo is making good progress on the vault, but that Heinrich's bag of detonators has been taken by John. He orders Fritz to retrieve the detonators. Al radios John, who briefly explains what is happening. Deputy Police Chief Dwayne T. Robinson arrives, insults Al, and takes command.
Hans, who has chosen Holly's office as a command post, is approached by Holly who makes two simple demands: a couch for Ginny and that the terrorists let the hostages use the bathroom. She makes sure to use "Gennero" so that she can't be linked to John. Argyle turns on the TV in the limo and notices that the building he is in is under siege. He looks for an exit from the garage but finds himself trapped, but turns on his CV radio to overhear John and Al's conversation. The police set up spotlights and send a four man SWAT team to enter the building. They are Rivers, Rodriguez, and two unidentified SWATs. John is recommended by Al to sit tight, but he knows the terrorists have extremely heavy artillery. Uli and Eddie fire at the team as they try to break in the front door so the police department sends in an RV to rescue the men (and break into the front entrance). Hans orders James and Alexander to take down the tank with a rocket launcher. He then orders them to hit it with another rocket, upsetting John enough to throw some C4 down the elevator shaft, blowing up the entire second floor and killing James and Alexander.
The police and Thornburg look on in amazement. Deputy Robinson takes the radio from Al, but John insults him and informs him that he will only speak with Al. Back in the foyer, Harry is getting antsy so he snorts more cocaine and gets up to talk to Hans. He tells Hans that he can get John to cooperate. He gives Hans John's name and occupation and uses Hans' radio to talk to John. Thornburg sends an assistant to look up McClane's information while Harry tries to convince John to give over the detonators. Harry pretends that he is John's good friend but he doesn't recognize that Hans plans to kill him if John didn't cooperate. John struggles to barter with Hans to spare Harry, but Harry sticks to pretending. John refuses to respond to Harry's friendly requests to give back the detonators so Hans fatally shoots Harry.
Everyone inside and outside the building is shocked. Robinson dismisses Al to go home, but he refuses to leave until the situation is resolved. Robinson believes Harry would still be alive if John turned himself if, but John radios back with his own opinion on the matter. Hans finally addresses the police and begins to list the names of "fellow freedom fighters he wants released from prisons around the world. He also orders a helicopter to take him and the hostages to the airport. John and Al don't buy the story and realize that something else is afoot. Special Agent Johnson and Agent Johnson arrive from the FBI and take over control from Deputy Chief Robinson.
Hans inspects the explosives in the mechanical room and is cornered by John. He decides to pretend to be an escaped hostage and John believes it. On Floor 33 John gives him a handgun which Hans pulls on him instantly. John tries to get him to reveal his plan, but Hans pulls the trigger rather than spoiling his plot. The gun was never loaded, but before John can arrest or shoot Hans the elevator arrives with Karl, Franco and Fritz. John manages to shoot Fritz and Franco, but runs out of bullets. Hans, knowing John is barefoot, has Karl shoot the glass walls of the office John is trapped in. They use a flash grenade but John has vanished by the time the smoke has cleared. However, he was forced to leave the bag with the detonators.
Hans gives Uli the detonators and Karl smashes some decorations at the Christmas party. Holly celebrates his anger, taking it as a sign that John is still alive. John slinks into a bathroom with bloody feet which he begins to clean and bandage. Theo informs Hans that he has broken through the first six levels of the vault's security and that he is ready for Hans to disengage the final electromagnetic lock. Thornburg's assistant brings good news to Thornburg, telling him that she knows John McClane's records and his LA address. As Al tries to keep an injured John company over the radio, Theo and Hans realize that the FBI is planning on cutting the power to the building. Theo smiles, realizing that the electromagnetic lock will diengage when the power is cut. Special Agent Johnson instructs a power company worker to turn off the power for a ten block radius around Nakatomi. The FBI celebrates, Robinson worries that the mayor will be upset about the cut power, Al complains about the FBI's predictable behavior, and Hans and Theo celebrate as the vault opens.
John asks Al to tell his wife goodbye should anything happen to him, but Al tells him to pull through it. Thornburg arrives at Holly's house and threatens Paulina to let him talk to the children. John waddles back to the machinery room and finds the large amount of C4 wired to blow up the roof. He radios Al, but is caught by Karl. Karl takes John's radio and gun, but John throws a punch and the two begin to fistfight, agreeing that it is personal for both of them. Hans watches a small TV and recognizes the children Thornburg is interviewing. He then picks up the face-down family photo of the McClanes and approaches Holly. He fires the gun into the air, orders all the hostages to the roof, and takes Holly with him to the vault. She chastises him for being nothing but a crook when she realizes he's simply robbing the vault. Karl holds the upper hand of the fight, but John manages to get in some good hits. Karl is able to get his hands on a gun, fires, and grazes John's shoulder as he escapes through a doorway. Karl follows but John gets the upper hand, knocking the gun free. The two continue to wrestle and throw punches up a staircase until John wraps some chains around Karl's neck, pushing him over the railing. He then pulls the other end of the chain along a track, causing Karl's hanging body to zip across the room and slam into a wall. Karl hangs from the chain.
Two Army helicopters approach Nakatomi Plaza. Special Agent Johnson and Agent Johnson ride in one of them, commenting that they plan on ambushing the terrorists and that they would be happy with a 25% hostage loss rate. Uli and Eddie usher all the hostages to the roof, and John shoots Uli as he chases the hostages, searching for Holly. Ginny tells John that Holly is with Hans. Trying to warn the helicopter not to land and to get the hostages away from the explosives, John begins firing Uli's machine gun in the air. The hostages run back down into the building, but the FBI in the chopper begins firing at John. He manages to make it to a slightly hidden edge, and uses a fire hose to repel down the building. As he jumps, Eddie informs Hans that the hostages have returned to the 30th Floor in a panic, so Hans pushes the trigger for the explosives. The explosion engulfs the FBI helicopter, killing both Agent Johnsons and everyone onboard. The fire hose reel snaps from the wall and follows John off the roof. He manages to shoot through a window and land before it falls, but after it passes his floor the weight of the reel starts to pull him out of the window. He manages to untie the hose in time.
The helicopter falls and explodes the the 30th and surrounding floors, setting the foyer on fire. The elevator is affected by the blast and blows out the wall of the 30th floor. John follows his wife's screams to the vault, where Hans is in a hurry to finish loading all the bearer bonds. Along the way he notices a mail cart with tape and other supplies and discovers he only has two bullets left. In the garage, Argyle notices Theo unloading an ambulance from the back of the courier truck. He rams the ambulance with his limo, then rushes to the car and punches out Theo.
As Kristoff runs a stack of bonds down the hallway, John knocks him out. He slowly walks down the hallway toward Hans, Eddie, and Holly. Hans holds a gun to Holly's head and orders John to drop his weapon. Eddie picks up another machine gun, but Hans instructs him not to shoot. Hans mocks John for being a cowboy, and points his gun toward him. John holds his hands behind his head and starts laughing, and Hans and Eddie join in, knowing his situation is futile. At that moment, John grabs his handgun which is taped to his back, fires one shot at Eddie, killing him; and another at Hans, hitting him in the shoulder. Hans falls out the window but manages to hold onto Holly's new Rolex. Hans slowly aims his gun at Holly, but John manages to unclasp the watch, sending Hans plummeting to the ground.
In the rubble outside, John meets Al and they both hug and thank each other. Robinson approaches and chews out McClane for the damage of the building. A not-quite-dead Karl arises to screams and aims a gun at John and Holly. Everyone falls to the ground by Al, who fires his sidearm, killing Karl. Argyle rams his limo through the garage's gate, and John and Holly walk toward his limo. On the way they are stopped by Thornburg for an interview. Holly punches him in the face and the couple continues to the limo, kissing as Argyle drives away from a damaged and burning Nakatomi Plaza.