Murtaugh turns to Cole's former mentor, Tom Barnes, for help on a high-stakes cartel case. Meanwhile, Murtaugh and Trish meet Natalie and Maya for the first time, and tensions mount between Bailey and "The Gute", as the new partners begin to work together.
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.