In the late summer of 1994 in New York City, five years after the events of Die Hard 2, the Bonwit Teller department store is destroyed by a bomb during the morning commute. The New York City Police Department gets a call from “Simon” claiming responsibility. Simon threatens to detonate another bomb unless suspended police officer Lt. John McClane is dropped in Harlem, a primarily black neighborhood, wearing only his underwear and a sandwich board with “I Hate Niggers” written on it; the NYPD complies. McClane is saved from an angry group of black men by Zeus Carver, a nearby electrician and shop owner. McClane and Carver retreat to NYPD’s headquarters, where they learn that a large quantity of binary liquid explosives, which caused the Bonwit explosion, were recently stolen. Simon calls again and demands that both McClane and Carver follow his continuing instructions.
Simon sends the two on a series of children’s riddles, which ultimately require them to reach the Wall Street subway station 90 blocks south within 30 minutes to stop a bomb planted on a Brooklyn-bound 3 train. McClane boards the subway while Carver drives to the stop. Though Carver answers Simon’s call and McClane locates the bomb, Simon detonates it immediately after McClane throws it off the train in the station, derailing the train and damaging the subway station. As McClane and Carver regroup with the police, they are met by FBI agents, who reveal Simon is “Peter Krieg”, a former colonel in the East German People’s Army and a mercenary-for-hire. However, Krieg’s real name is Simon Peter Gruber, the brother of Hans Gruber, whom McClane had killed years earlier in Los Angeles.
Simon then calls the police, knowing the FBI is there, to inform them that he has placed a bomb in a NYC public school that is rigged with a radio detonator triggered by the use of the FBI and police bands. Simon tells them that he will give McClane and Carver the school’s location if they continue to play his games, but threatens that evacuating any school will lead to the device detonating. While McClane and Carver set off on Simon’s next task, the police organize all NYC’s public works to search schools, using 9-1-1 to coordinate activities. As McClane and Carver solve Simon’s riddles, McClane realizes that Simon is using the school bomb as a distraction to draw the police away from the bomb damage at Wall Street. They return there to find that Simon and his team used fake repair crews to dig into the Federal Reserve Bank of New York and steal $140 billion of gold bullion in dump trucks. They follow the trucks to an aqueduct in the New York City Water Tunnel No. 3. McClane has Carver continue Simon’s game while he follows the trucks.
Within the tunnel McClane kills some of Simon’s men, discovering they have a pre-wrapped roll of quarters on them. Simon destroys a cofferdam, flooding the tunnel, but McClane escapes through a vent, ending up near Carver. After surviving a car chase with Simon’s men who had followed Carver and finding that they also had a pre-wrapped roll of quarters, they realize that the roll of quarters would pay for a toll bridge, and they head to a tanker vessel in the Long Island Sound. They sneak aboard, learning that the bullion isn’t there, but are both captured.
Simon confirms McClane’s suspicions that the school bomb (which had been found using the clues provided by Simon, but turned out to be a dummy) was a trick to distract police before handcuffing the two to the real bomb. He says he is going to destroy the tanker, redistributing the bullion across the Sound, to destroy the economies of the world. Before Simon leaves, McClane jokingly asks him for some aspirin for his hangover, much to Simon’s amusement. He happens to have a bottle of aspirin and tosses it to McClane. After Simon leaves, McClane passes a cable splinter to Carver, who picks the handcuffs to free them. They barely escape before the bomb detonates, sinking the tanker.
As McClane and Carver are debriefed by the police, McClane reports that none of the bullion was on the tanker. McClane notices the bottle of aspirin came from a truckstop located in Quebec at the Canada-US border. McClane, Carver, and the police arrive at a warehouse near the truckstop where Simon and his men are in the process of distributing the bullion and planning their escape. The rest of Simon’s men are captured, while Simon and his girlfriend Katya attempt to escape in a helicopter, stopping to fire upon McClane and Carver. McClane, armed only with a small revolver, shoots an overhead power line that falls onto the helicopter, crashing it and killing Simon and Katya. Carver then convinces McClane to call his estranged wife, Holly.