Riggs and Murtaugh are led into the underground mob world as they investigate a murder in a hospital. Meanwhile, Murtaugh learns that Riana is secretly dating his neighbor and nemesis' son. Also, Riggs spends more time with his childhood friend, Molly, and Scorsese's real name is revealed.

It's Christmas time and the Murtaugh family is headed to Hawaii. However, Murtaugh's vacation is put on hold when he and Riggs are called to a homicide and the victim is an old friend. Meanwhile, Riggs gets a surprise phone call from a relative just in time for Christmas.