As Sergeant Roger Murtaugh (Danny Glover) and his partner Martin Riggs (Mel Gibson) prepare to retire from the force, their plans are abruptly interrupted when they fail to disarm a bomb at a local office building. The fallout from this incident is rapid and punishing, leading to their demotion and assignment to patrolling the streets of Los Angeles. It is during one of these mundane patrols that they stumble upon the audacious theft of an armored car, with the spirited Delores at the wheel of the getaway vehicle.
This daring heist leads Murtaugh and Riggs to a key suspect, who points them to the diabolical Jack Travis, a once-respected LAPD lieutenant who has now turned into a ruthless arms smuggler. The department is thrown into chaos when they learn that the stolen equipment includes armor-piercing bullets, raising the urgency for Murtaugh and Riggs as they delve deeper into this criminal web.
Just as Murtaugh and Riggs are starting to regain their footing, they've been reinstated, this time teaming up with Sergeant Lorna Cole (Rene Russo) from internal affairs to hunt down Travis. Unbeknownst to them, Travis is busy making dodgy deals with the infamous mob boss Tyrone, leading to the untimely end of one of the armored car thieves who had the misfortune of being caught by him.
In a cunning move, Travis exploits his former police credentials to infiltrate an interrogation room, ensuring that the suspect in custody is silenced before he can unveil crucial information. Meanwhile, Sergeant Cole has managed to confirm Travis's identity through surveillance footage, setting off a thrilling chase between the two sides that oscillates between clever tactics and explosive confrontations.
As Riggs, Murtaugh, and their old friend Leo Getz (portrayed by Joe Pesci) race against time to locate Travis, they encounter several heart-stopping moments, including a nail-biting incident during a hockey game where Getz finds himself caught in a dangerous crossfire. Nevertheless, he provides invaluable information regarding a warehouse that Travis is suspected of using as the center of his unlawful operations.
While waiting for backup from Cole at a local food truck, Murtaugh and Riggs inadvertently interrupt a drug deal. Responding swiftly, Murtaugh displays his quick reflexes and manages to apprehend one of the armed offenders. However, the situation takes a personal turn when Murtaugh discovers that the assailant, Darryl, had a close connection to his son, Nick, throwing him into emotional turmoil. As Murtaugh grapples with this revelation, Riggs and Cole focus on securing the next arms shipment at the warehouse without complications.
That evening, Riggs and Cole share a moment of vulnerability that leads to a romantic entanglement, but their bliss is short-lived as the harsh realities of their work come crashing back. The next day, Murtaugh and Riggs console one another after attending Darryl's funeral, where the grief-stricken father beseeches Murtaugh to seek justice against those who supplied his son with the gun that led to his tragic fate.
Diving deeper into the case, Cole uncovers a startling revelation: the arms shipment they had seized was originally meant for destruction but had been stolen from police custody. This revelation leads them to nullify Travis's credentials and link him to Tyrone, who, during interrogation, divulges critical information regarding an auto garage that serves as a cover for his operations. Riggs, Murtaugh, and Cole bravely infiltrate the establishment, apprehending several of Tyrone's dangerous henchmen.
Meanwhile, Travis manipulates his gang to hack into the police system in search of another arms storage site, forcing Captain Murphy to aid him against his will. As Cole discovers the computer breach and Murphy's mysterious disappearance, she joins forces with Riggs, Murtaugh, and a rookie officer named Edwards, who looks up to the seasoned detectives for guidance. They act swiftly to thwart Travis's plans and rescue Murphy, unfortunately losing Edwards in the line of duty during the chaotic scramble.
Following this intense confrontation, Getz delivers crucial information regarding a housing project owned by Travis's front company. Together, Riggs, Murtaugh, and Cole launch a nighttime raid to infiltrate the site, stirring up a massive firefight in which Riggs sets the construction area ablaze, resulting in high casualties among Travis's crew. In a heart-stopping climax, Murtaugh seizes the chance to toss Darryl's gun loaded with armor-piercing rounds to Riggs, who takes aim and finally brings Travis down with a well-placed shot.
With Cole being evacuated via helicopter due to her injuries, Riggs confesses his deep feelings for her, laying bare his emotions in a moment of vulnerability. In the wake of these harrowing events, Murtaugh's family gathers to celebrate a significant milestone - his long-awaited retirement. However, amidst the jubilation, Murtaugh drops a bombshell on Getz: he decides against cashing in on his dream home and instead opts to remain active on the force, cherishing his partnership with Riggs, the unpredictable yet endearing warrior. Following this announcement, Getz unveils his own surprising news: he has found love with Cole, a twist that leaves everyone in awe, encapsulating the complex emotions that define both their lives and careers.
