Lethal Weapon 4 is a 1998 American buddy cop action film directed and produced by Richard Donner, and starring Mel Gibson, Danny Glover, Joe Pesci, Rene Russo, Chris Rock, and Jet Li (in his American film debut). It is the fourth and final instalment in the Lethal Weapon series.
Lorna Cole is pregnant with Martin Riggs' baby; they are not married, but both are thinking about it a tough time and have misgivings and fears. Roger Murtaugh's daughter, Rianne Butters, is also pregnant and has secretly married Lee Butters, a young cop who works at the same precinct as Murtaugh and Riggs, though she cannot tell her father because he doesn't want her to date cops.
The opening scene is an unrelated sequence in which Riggs and Murtaugh, two LAPD sergeants, confront a lunatic wearing a flame-retardant armoured suit and wielding an automatic firearm and a flamethrower. The unidentified man is destroying cars and shops along a city street. Aside from some comedic value and a reminder to the audience of Riggs marksmanship skills, the scene mainly serves to show the two partners informing each other of Lorna's and Rianne's pregnancies. There, Murtaugh is in his boxers for distraction of the lunatic, with Riggs shooting the napalm valve causing it to go out of control and go flying straight into a gas truck, thus blowing up to smithereens with the truck and landing on Riggs and Murtaugh's car blowing it up in the process, leaving Riggs and Murtaugh to walk on foot. After this scene, a title card shifts the story to "almost nine months later."
The rest of the movie revolves around Riggs, Murtaugh, and Butters' investigation of a Chinese immigrant smuggling ring, which begins after a vessel is captured with a cargo hold of slave labor. That night, Murtaugh, Riggs, and Leo Getz - the latter now a private detective - find a small dinghy alongside with an entire Chinese family, whom he "rescues" and provides shelter for at his house, claiming to be "freeing slaves." Meanwhile, Riggs and Murtaugh are being informed by Captain Murphy that the damage they've caused, the department lost it's insurance and aren't able to get a new one, and since firing them isn't really an option for them, they're being promoted to Captain.
Information about a crime boss known as Uncle Benny Chan then leads them to Chinatown, where they are introduced to their new arch-nemesis, a high-ranking Triad negotiator named Wah Sing Ku. Wah Sing Ku is organizing the release from prison of four Triad overlords, called the Four Fathers. They are being held by a corrupt Chinese general who demands a huge payoff in exchange for their freedom, but Uncle Benny and Wah Sing Ku have plans to give him counterfeit money instead. The captive artist working on the printing plates for the scam is the elder uncle to Hong, the father of the Chinese family Murtaugh has rescued.
Riggs and Murtaugh decide to hire Leo to follow Uncle Benny around, but the Triads feels they are getting too close and decides to strike back. After Hong contacts his uncle, Riggs and Murtaugh come home to find Wah Sing Ku there with the other Triad gang members holding Murtaugh's family hostage; Hong and his family were already kidnapped. After a brief skirmish (where Wah Sing Ku dismantles Riggs' gun with a flick of his wrist in one deft move), the entire family is tied up and left to die in the house as it is set on fire with everyone inside, including both pregnant women. Ping, the youngest of the Hong children, comes out from hiding safely and cuts them loose setting them free just in time to break out through the living room window.
Riggs takes a radio from Lorna's car, and the pair set off with Rianne's car in hot pursuit of two of the Triad men. Reaching them on the freeway, Riggs lets Murtaugh take over driving and climbs out of the car and leaps over to a mobile home. He pulls one of the thugs through the car window into it, demanding to know where the Hongs are. After engaging in a fight they crash onto the road; Riggs, sitting on a table, holds onto the trailer by the plastic covering they fell through, and the Triad man is run over by a bus. His partner accelerates and attempts to kill Riggs, who is forced to throw one of the table legs at the assailant. Murtaugh rams into the Triads car' and, hearing sirens, the thug makes an escape. Riggs climbs back beside Murtaugh, and they chase the thug, trying to find answers. However, they accidentally fly off a ramp into a building, driving through one of the floors and out back onto the road. Then the last Triad man they know of is killed by a truck.
Leo alerts them that he had tracked down Uncle Benny at his dentist's office, and while using Leo as a distraction to keep the dentist busy, Riggs, Murtaugh, and Butters use laughing gas to extract the truth from him on where the Hongs are at. Here, Murtaugh inadvertently learns that Butters is married to his daughter and that he is the father of her baby, but puts it aside until later. Uncle Benny mentions the Four Fathers, which the detectives mishear as "forefathers"; another detective, Detective Ng, who knows about Chinese society and cultures, corrects them on this point and helps them piece the entire operation together. Benny is later strangled to death by Wah Sing Ku for his indiscretion, and Hong is killed as an example to get his uncle to cooperate. Even when the printing plates are finished, the uncle is killed as well for no information to given to the cops about what went on at the hideout.
Arriving at the meeting between the Triads and the corrupt general and his men, Riggs, Murtaugh, Butters and several other detectives reveal to the general and his men that the money that is being given him for the release of the Four Fathers is counterfeit. As a result, the general personally executes three of the Four Fathers. Wah Sing Ku's henchmen shoots and kills the general, and a gunfight breaks out between the cops, the Triads, and the general's private army in the foreign trade zone down by the docks. During the fight, one of the Four Fathers and older brother to Wah Sing Ku is killed by Murtaugh, and Butters is injured while protecting Murtaugh. The climactic scene takes place on a pier where Riggs and Murtaugh, both unarmed, take on Wah Sing Ku, who is enraged by the death of his brother. Eventually, while Ku nearly kills Riggs by choking him, Murtaugh impales Ku with a piece of metal stick. Murtaugh is knocked out unconscious by Ku, and Riggs and Ku fall into the water as the concrete pier collapses. Ku, after getting brutally beaten as well as impaled, is finally killed by a desperate Riggs with a submerged AK-47 nearby. Riggs swims up to the surface, but becomes trapped underwater again, under a part of the broken pier. Murtaugh comes to his senses regaining his consciousness, and realizes Riggs is in the water and dives in to pull the broken part of the pier on him and rescues him.
The next scene shows Riggs at his deceased wife Victoria Riggs' grave telling her he hasn't visited her in a while (evident from a weed growing over the grave), and confesses to her of his love for Lorna. He asks her for help and support in marrying Lorna as he tells her she would've wanted him to be happy and be married again and make Lorna happy as he made her happy when they were married. He then suddenly draws his gun when he hears a nearby footsteps in the cemetery, which turned out to be Leo Getz practicing his PI techniques. Leo tells Riggs an emotional story of his life and how that he and Murtaugh are the only real friends he's ever had aside from his childhood pet frog, and how they're like family to him. Riggs' pager reveals indicating that it's a message from Lorna that she's about to have the baby and they rush to the hospital. Before leaving the grave, Riggs tells Victoria that he'll always have the ring she gave him, and always have her in his heart and memories.
The movie ends with Lorna and Martin's last-ditch marriage by a minister, Rabbi Gelb, in the maternity ward, and Roger accepting Lee as his son-in-law, as well as his and Rianne's marriage. Two babies are born to Rianne and Lorna, as Martin Riggs is finally settling down. Captain Ed Murphy gives them their former positions as sergeants back since the city is self-insured, and brings gifts for the new-born babies. The Hong family is finally granted asylum. Everyone in the maternity ward is all getting their picture taken by the doctor for the family. The end credits feature the song "Why Can't We Be Friends?" by War along with a collage of screen shots and snapshots taken during production from all four movies, signifying the end of the series.
- Mel Gibson as Martin Riggs
- Danny Glover as Roger Murtaugh
- Jet Li as Wah Sing Ku
- Joe Pesci as Leo Getz
- Chris Rock as Lee Butters
- Traci Wolfe as Rianne Murtaugh
- Rene Russo as Lorna Cole
- Eddy Ko as Hong
- Conan Hutch Lee as Michael Sing Ku
- Steven Lam as Ping Hong
- Kim Chan as Benny Chan
- Ebonie Smith as Carrie Murtaugh
- Zu-Wu Qian as Chung Hong
- George Kee Cheung as Fan
- Calvin Jung as Paul Ng
- Roger Yuan as Chu
- Steve Kahan as Ed Murphy
- Darlene Love as Trish Murtaugh
- Phil Chong as Yee
- Jack Kehler as Mr. Proody
- James Wing Woo as James Wing Chow
- Raymond Ma as Dr. Cheng
- Mary Ellen Trainor as Stephanie Woods
- François Chau as Li Lum Chung
- Raymond Moy as Fan Wong
- Danny Wynands as Man with Flamethrower
- This is the final film in the Lethal Weapon franchise.
- This is Jet Li's first acting debut.
- This is the first time Riggs isn't seen smoking, following the third film, it is presumed that he stopped smoking from then on.