Buttoned-down veteran LAPD detective Roger Murtaugh is partnered with unhinged cop Martin Riggs, who — distraught after his wife's death — has a death wish and takes unnecessary risks with criminals at every turn. The odd couple embark on their first homicide investigation as partners, involving a young woman known to Murtaugh with ties to a drug and prostitution ring.

Riggs and Murtaugh are on the trail of South African diplomats using their immunity to engage in criminal activities.

Riggs and Murtaugh pursue a former officer who uses his knowledge of police procedure and policies to steal and sell confiscated guns and ammunition to local street gangs.

With personal crises and age weighing in on them, Riggs and Murtaugh must contend with deadly Chinese triads trying to free their former leaders from prison and onto American soil.