Riggs and Murtaugh are on the rainy streets of downtown Los Angeles where they confront the "Human Tank", a man dressed in aluminum armor gear with a flamethrower attached to him and wielding a machine gun. Riggs finds that the armor is bulletproof when they had open fire. Murtaugh tells Riggs that Lorna is pregnant. In response, Riggs tells that Murtaugh's daughter Rianne, is pregnant. To distract the Human Tank, Riggs has Murtaugh strip down to his underwear. Murtaugh clucks chicken noises, gaining The Human Tank's attention. Riggs manages to shoot the flamethrower, sending The Human Tank to a gas station, killing him. They both leave the scene.
Almost Nine Months Later...Edit
Riggs and Murtaugh are on the boat with Leo, who had accidentally caught a shark. When they exchange about themselves, Riggs warns Murtaugh about Leo attempting to shoot the shark. Riggs confiscates his gun and throws it overboard. When a ship comes nearby, gunshots is heard. When goons on the ship shoots at them, Riggs climbs onboard, where he confronts the cargo ship captain. The captain escapes and Riggs finds poor Chinese immigrants under the ship. At the crime scene, Riggs and Murtaugh encounters Detective Butters. After Butters' sensetive side shows that he doesn't appreciate innocents being executed, Riggs departs from the scene to go to a restaraunt.
The next day, he arrives back home where Lorna is at - who is officially pregnant. During a conversation at a walk on the beach, she accidentally reveals that Butters is the father of Rianne's unborn child. The couple arrives at Murtaugh's home, where they discover that Murtaugh are keeping the Hongs, an immigrant family who were smuggled to the United States for work. The duo leaves for work. Captain Murphy assigns them to the ranks of "Captains" after the LAPD lost their insurance carrier due to their recklessness from previous adventures. They both go with Butters, who seems to acknowledge the two for their ranks. After a brief encounter with Leo, they depart to a Chinese restaraunt where Chinese crime boss Uncle Benny is hidden. They ask for information but Benny refuses, so the trio leaves in causing trouble. Therefore, Riggs confronts the captain of the cargo ship and chases him. However, he escapes again and Riggs are forced to let go of another suspect.
The next day, Riggs is having a boxing match. After faking his loose shoulder, Riggs agrees with Murtaugh about their adventures when they became partners.
At the police station, Riggs insults Leo who had arrived at the police station and learning that the Triad captain was found dead on a rooftop before departing to Murtaugh's home.
There, they find Triads and Wah Sing Ku, Uncle Benny's ruthless henchman there. After being knocked down by Wah Sing Ku's crafty manipulation, the duo, alongside Lorna, Rianne and Trish are tied up and left for dead. Fortunately, they are set free by Ping, the Hongs' youngest family member.
Riggs and Murtaugh goes to a highway to find Wei and Yee, Ku's henchmen. Riggs climbs into a trailer and drags Wei in for information, but to no avail. Wei is killed and Yee is left. Riggs and Murtaugh chases Yee but the latter is soon killed by a semi-truck, leaving to the fact that they do not have no information about the Triads.
After returning to the burning house, Butters arrives. Riggs gets a call from Leo and the trio leaves to find Uncle Benny at the dentist office, with Leo distracting the dentists. However, when confronting Benny, they accidentally inhale nitroxide gas, causing the trio to laugh hysterically and cracking few jokes, though they gain few information from Benny. When leaving, Riggs is punched by Murtaugh for keeping Rianne's secret.
At the crime scene of the laundered money, Riggs finds that the 'forefathers' are actually the "Four Fathers", four top-ranking Triads based in Hong Kong and that the Triads are buying their release.
The trio, alongside an Asian police officer Detective Ng and another detective, arrives at the exchange to reveal that the Chinese money is counterfeit. This prompts a shootout, during the shootout, Murtaugh accidentally kills one of the Four Fathers - Michael Ku, Wah Sing Ku's older brother.
Then, the duo confront Wah Sing Ku. They fight off him but they are beaten senseless. After headbutting Ku, Riggs resets his arm and gains the upperhand on him but Ku overpowers soon and nearly kills Riggs by choking him. However, Murtaugh interferes and impales Wah. The two struggle underwater but Riggs manages to shoot and kill Wah Sing Ku with multiple gunshot wounds to the chest. Riggs nearly drowns when the pier collapses on him but Murtaugh manages to save his life.
At Victoria's grave, he encounters Leo. Leo coax with Riggs by telling he and Murtaugh are good friends and are treated as family. Riggs then gets a message from Lorna that she is in labor. At the hospital, he and Lorna officially gets married and the couple collides with Murtaugh and Leo to become an official family.