Martin Riggs, a one-man killing machine, is a Los Angeles policeman who recently lost his wife and has been acting increasingly unstable. Roger Murtaugh is a by-the-book homicide detective with an impeccable record and a loving family. Now the two are stuck with each other as partners, investigating a suicide that leads to an international crime ring and ever-increasing danger.
Riggs and Murtaugh are on the trail of South African diplomats who are using their immunity to engage in criminal activities.
Martin Riggs and Roger Murtaugh pursue a former LAPD officer who uses his knowledge of police procedure and policies to steal and sell confiscated guns and ammunition to local street gangs.
Lorna Cole is pregnant with Los Angeles Police Department Sergeant Martin Riggs' baby; they are not married, but both are thinking about it. LAPD Sergeant Roger Murtaugh's daughter Rianne, is also pregnant, though he is not told the child is with Detective Lee Butters since he did not want his daughter to marry a police officer. Due to issues with the department's insurance carrier over Riggs and Murtaugh's actions as sergeants, Captain Murphy promotes them to captains.