LAPD sergeant Roger Murtaugh, his partner, sergeant Martin Riggs, and their friend Leo Getz, who is now a private investigator, are out on Murtaugh's boat, fishing in the Los Angeles Harbor, when...

LAPD sergeant Roger Murtaugh, his partner, sergeant Martin Riggs, and their friend Leo Getz, who is now a private investigator, are out on Murtaugh's boat, fishing in the Los Angeles Harbor, when they are sideswiped by a huge freighter. After a wild gunfight against a group of Chinese men who were on the freighter, it is discovered that the freighter is full of illegal Chinese immigrants. As Murtaugh sulks over what is left of his now sunken yacht, he discovers a hidden Chinese immigrant family and their patriarch, Mr. Hong, and decides to take them in. At the police station, Detective Ng expresses his belief that Chinatown crime boss Benny "Uncle Benny" Chan is behind the smuggling. Sergeant Lorna Cole of the Internal Affairs Division is unable to help out on the case because she is pregnant with Riggs's baby, and Murtaugh's daughter Rianne is also pregnant. Helping Riggs, Murtaugh, and Leo on the case is Sergeant Lee Butters, the father of Rianne's baby. Wah Sing Ku, a leader in the Chinese Triads, is angry about the disappearance of the Hong family, the family Murtaugh took in, and Wah Sing Ku and the triads are the most dangerous enemies that Riggs and Murtaugh will ever face together. Wah Sing Ku and his men show up at the Murtaugh house, take the Hongs, and set the house on fire with Riggs, Lorna, Murtaugh, Rianne, Murtaugh's wife Trish, Murtaugh's other daughter Carrie, and his son Nick inside. Unknown to Wah Sing Ku, little Ping, the youngest member of the Hong family, was left behind in the house. Ping frees Riggs, who frees the others. Later, when Riggs, Murtaugh, Butters, and Lorna discover that Wah Sing Ku has killed Mr. Hong, Mr. Hong's uncle, and Uncle Benny Chan, Roger takes it very personally because Hong and Hong's uncle were killed.