A slightly unhinged cop is partnered with a veteran detective trying to maintain a low stress level in his life.
Former international CIA operative Wesley Cole returns home and assumes duty as a police officer with the LAPD. Cole will find himself navigating a new partnership with Murtaugh, as he adjusts to life in Los Angeles. Meanwhile, Avery continues his campaign for city council.
Against Murtaugh's advice, Cole reaches out to Tom Barnes to help with a case that hits close to home, putting Murtaugh and Cole's partnership to the test. Meanwhile, Trish prepares to announce her campaign for District Attorney.
When Riggs and Murtaugh attend Leo Getz's surprise wedding, they end up investigating a missing person. Then, Riggs comes face to face with someone from his past and Murtaugh receives news that might change his life forever.
While Cole gets into the holiday spirit for his first Christmas with Maya, Murtaugh hopes he can convince RJ to come back home from Costa Rica for the holidays. At the precinct, Cole and Murtaugh are saddled with a complicated burglary and home invasion case. Meanwhile, Avery's holidays are a bit blue, and Bailey is still trying to figure out her new partner.
Cole juggles the realities of his job and his duty to be a good parent, as he and Murtaugh work together to bust a gang running a lottery scam. Murtaugh gets ready to celebrate his 30th anniversary with the LAPD and receives a surprise visit from his competitive father-in-law, Don Bennett.
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.
Murtaugh and Cole investigate after a robbery of a truck filled with fine art. Cole deals with lingering feelings for Natalie after a development in her life. Meanwhile, Riana blackmails Murtaugh into letting her go to a concert after she catches him in a lie he told Trish.
Cole reflects upon his time working for the CIA, as a person from the past makes a startling reappearance. Murtaugh struggles with his own mistakes, after a murder raises questions about a suspect he put away years prior. Meanwhile, Leo Getz returns as the attorney on the case and tries to convince Trish to join his team.
When Riggs visits his father-in-law in prison, a walk down memory lane reveals an old secret about his deceased wife. Meanwhile Murtaugh tries to impress Captain Avery, and, united by the death of a mutual friend, Trish and Leo Getz try and solve a murder on their own
Cole finds himself on the rebound after Natalie's engagement, and his new romantic interest, Julie, has an unexpected connection to A.D.A. Erica, complicating things at work. Meanwhile, Murtaugh worries about the connection between the murder he's investigating and a new opportunity for Trish to serve as co-counsel on a high-profile lawsuit with Leo Getz.
Riggs and Murtaugh investigate the death of a surfer. Meanwhile, Murtaugh grows suspicious of Trish's new friend, with whom she's been working on a charity event - and then learns it's NBA champion Scottie Pippen. Also, Riggs has violent nightmares that bring up scars from his childhood.
Riggs and Murtaugh are thrown into the world of counterfeit money. When a group of teenagers inadvertently gets involved, it strikes a chord with Murtaugh, who is dealing with his own issues regarding his son, RJ. Meanwhile, Riggs decides to pay a visit to someone from his past.
The duo sets out to unlock a case about a veteran hitman who Murtaugh has followed for years. Meanwhile, Riggs struggles to find a connection with his father, Murtaugh scares Riana with his overprotective driving lessons, and the team finds themselves wedged in a dangerous incident that tests their trust.
Cole confronts his past when his former mentor, Tom Barnes, delivers alarming news, as he and Murtaugh investigate a robbery of safe deposit boxes. Meanwhile, Murtaugh clashes with Trish's new client, Louie Gutierrez aka "The Gute" and enlists Bailey's help to investigate her.
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.
New partners Murtaugh and Cole attempt to find a steady rhythm as they work to solve the murder of a finance executive. Meanwhile, Cole navigates his role with his ex, Natalie, and his daughter, Maya, and Avery grapples with the outcome of his campaign for city council.
When Cole and Murtaugh investigate a case involving a father and daughter crossing the Mexican border, they end up uncovering a major issue with California Boarder Patrol. Meanwhile, Trish prepares her campaign for D.A. and must face parts of her past, before they find their way into the media spotlight. Cole also confronts his past when he experiences flashbacks as a result of an injury.
After the city's gun buy-back program is robbed, the team is on a hunt for those responsible. Meanwhile, Murtaugh walks on thin ice with Trish, Riggs finds an unlikely friend in Ruthie, and Captain Avery is reunited with a college "frenemy" who has key information about the case.
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.
Murtaugh and Riggs investigate a death that occurs moments before the victim's bet wins a horse race. Leo Getz insists it's a homicide and aids in the investigation. Meanwhile, Murtaugh updates his will, while Riggs struggles to come to terms with his past.
Murtaugh and Riggs search for the culprit of a local jewelry heist. Meanwhile, Murtaugh gets called "grandpa" by another parent while at the playground with Harper, sending him into a tizzy, and Riggs deals with withdrawal from drinking.
Riggs and Murtaugh are drawn into a fatal world of conspiracy theories. Meanwhile, Riggs' relationship with Molly evolves and Murtaugh and Trish attempt to get Harper into a fancy pre-school.
Cole wants to talk to Natalie about their relationship before it's too late, but a wrench is thrown in his plans after he bumps into a new ADA, Erica. Meanwhile, after being kicked out of the house for Trish's girl's night, Murtaugh finds himself an unlikely friend.
After the fatal end to an argument on a construction site, the squad works to untangle facts about the incident. Meanwhile, Riggs struggles to rekindle his relationship with Molly, Trish's job is on the line as she tries to close a big deal at work, and Murtaugh gets one last chance to make it right at home.
On Murtaugh's first day on the job as interim captain, the wife of a popular businessman is abducted and the squad finds a connection in the case to Riggs' father. Meanwhile, Riggs is left to grapple with his family and work.