A slightly unhinged former Navy SEAL lands a job as a police officer in Los Angeles where he's partnered with a veteran detective trying to keep maintain a low stress level in his life.
A noise complaint at a boxer's home leads Riggs and Murtaugh to a case involving illegal gun runners and Riggs becomes personally invested in the outcome when one of their targets reminds him of his late wife. Meanwhile, Trish worries about Murtaugh's health.
Riggs and Murtaugh investigate a violent case involving a drug cartel, two killings, theft, and Murtaugh's old T.O., Ned Brower, Trish and Murtaugh struggle to find time along.
A string of burglaries hits close to home for Murtaugh when one occurs in his own neighborhood, and it gets just as personal for Riggs when another break-in ends in a casualty. Meanwhile, Roger Junior connects with an old friend who might be twisted up in some criminal action of his own.
Murtaugh delves deep into the psyche of a former navy seal who is wanted for criminal activity, and draws parallels between him and his partner, Riggs, who also served in the military. Riggs' connection to the suspect threatens to interfere with the case, but it also forces him to open up to Murtaugh.
When Riggs and Murtaugh investigate a high-profile case surrounding the murder of a young model, they uncover a vicious secret behind the locked mansion gates of one of LA's wealthiest families. Riggs gets a jolt from his past when he discovers that an old friend of his wife has ties to the case. Murtaugh is shocked to hear that his daughter is sending promiscuous photos to her new boyfriend.
Riggs and Murtaugh look into the murder of one of L.A.'s fashion expeditors and discover an underground DEA operation. In other events, with Trish and the kids away, Murtaugh goes on a "bender"; and Riggs has all-too-real dreams of Miranda.
When a million dollar casino heist takes a deadly turn, Riggs befriends the only credible witness, an eight-year-old boy, and takes him into his care. Murtaugh pulls some dangerous stunts in an attempt to prove to everyone that he can be a motorcycle guy. Riggs contemplates what to do with the money he received from selling his home in Texas.
The whole precinct's holiday celebrations are cut short when they're called to examine a ruthless homicide linked to Eddie Flores (guest star Raul Casso), the deranged nephew of a notable drug lord who has a previous history with Riggs. The holiday season weighs heavily on Riggs, who flashes back to past Christmases with his former wife, Miranda. Murtaugh is also a little preoccupied with his neighbor's obnoxious holiday decorations.
Riggs and Murtaugh are caught in a turf war between a new generation of drug dealers and a Koreatown gang; Murtaugh is teamed with a temporary new partner; and Trish tries to set up Riggs with her co-worker.
Murtaugh and Riggs square off with the L.A. Sheriff's department when their investigation into the death of a Texas Ranger leads them to a possible misuse of power. The case also surfaces a dark secret from Capt. Avery's past.
When a car containing massive amounts of cocaine is stolen from an impound lot, Riggs and Murtaugh become embroiled in a notorious car theft ring. Meanwhile, Murtaugh experiences some frightening chest pains. If Riggs' driving isn't enough of a trigger, the lead defense attorney on the case is none other than the terrifyingly brilliant Trish Murtaug.
A series of violent crimes targeting members of the same church is investigated. Riggs, meanwhile, faces a moral dilemma when the one-year anniversary of Miranda's death sends him to a new low; and Trish and Roger disagree with RJ about his future.
A brutal car crash reveals that Cahill is the target of a murderous stalker, causing Riggs and Murtaugh to turn the tables and start asking her questions for a change. Meanwhile, after finding Murtaugh's file in Cahill's office, Riggs becomes obsessed with finding out about his past as Roger and Trish reel over their daughter's newfound fake ID.
Riggs and Murtaugh are forced to work with DEA agent Karen Palmer again, to protect Leo Getz, an ambulance-chasing attorney who was linked to the Cartel. As the three delve further into the case, they begin to realize that Leo may not be the only one with a target on his back. In the meantime, Riggs begins to view Agent Palmer in a new light while Murtaugh is left worried after Trish makes a spontaneous decision
A murder involving a high school football star draws Riggs and Murtaugh into the lucrative and corrupt world of college football recruiting; Murtaugh considers a change in his professional life; Riggs spends more time with Karen Palmer.
Riggs, Murtaugh and Palmer gain inside knowledge of dangerous new cartel operations, but Riggs' attachment to Palmer worries Avery and Delgado. In other events, Trish contemplates a new career opportunity.