After a mansion break-in turns into a homicide, Murtaugh and Riggs set out to find the culprit. Murtaugh and Trish question their trust in Riana as she gets into some trouble with new friends. Meanwhile, Riggs recalls his troubling childhood and finds a true family with Molly and Ben.

The squad is on high alert after an apparent threat is made on Riggs' life. With Murtaugh taking on more responsibility at work, he and Riggs have to deal with their changing relationship. Meanwhile, Trish gets caught up in some trouble and Molly asks Riggs to make a big decision about their future.