Murtaugh and Riggs respond to the murder of an escaped patient of Dr. Cahill's who mysteriously goes off the rails. The investigation brings to light a hidden scheme far bigger than they imagined. Meanwhile, Riggs' anger gets the better of him once again, causing Avery to consider whether or not he is fit to serve. Also, family tension runs high between Murtaugh and Trish, who have to make big decisions about R.J.
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.