Riggs and Murtaugh are drawn into a fatal world of conspiracy theories. Riggs' relationship with Molly evolves. Murtaugh and Trish attempt to get Harper into a fancy pre-school.

After the fatal end to an argument on a construction site, the squad works to untangle facts about the incident. 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. Murtaugh gets one last chance to make it right at home.

Murtaugh turns to Cole's former mentor for help on a high-stakes cartel case. Murtaugh and Trish meet Natalie and Maya for the first time. Tensions mount between Bailey and 'The Gute' as the new partners begin to work together.

When Cole is investigated by the FBI, Murtaugh is forced to question his loyalty to his own partner. Meanwhile, Cole works a case that puts Natalie's fiancé, Andrew, into the crosshairs right before their wedding day.