After the fatal end to an argument on a construction site, the squad works to untangle facts about the incident. Meanwhile, Riggs struggles to rekindle his relationship with Molly, Trish's job is on the line as she tries to close a big deal at work, and Murtaugh gets one last chance to make it right at home.
When Texas cop and former Navy SEAL Martin Riggs suffers the loss of his wife and baby, he moves to Los Angeles to start anew. There, he gets partnered with LAPD detective Roger Murtaugh, who, having recently suffered a "minor" heart attack, must avoid any stress in his life.
From the moment the brash and impulsive Riggs meets prudent, by-the-book Murtaugh, it seems as if this partnership is doomed. But after their first case together, both realise this arrangement might just work out after all - if only Riggs doesn't get them killed first.