Murtaugh and Cole try to find their stride as they work to solve the murder of a finance executive; Cole navigates his role with his ex, Natalie, and his daughter, Maya; Avery grapples with the outcome of his campaign for city council.
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 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.
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.
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 finds himself on the rebound after Natalie's engagement; Murtaugh worries about the connection between the murder he's investigating and an opportunity for Trish to serve as co-counsel on a high profile lawsuit with Leo Getz.
Murtaugh realizes his fighting movies aren't as sharp as they used to be when he and Cole investigate the murder of an underground MMA fighter; Trish considers running for public office; Cole and Erica try to keep things casual.
When Cole and Murtaugh investigate a case involving a father and daughter (illegally) 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.
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.