Hondo and Lina go undercover to infiltrate and take back a cruise ship that’s under siege by drug smugglers who will execute passengers if they detect police on board. Street enters the SWAT Training Academy and finds the competition fiercer than he expected.

Hondo has a tense reunion with a fellow Marine, Ruiz, when the team hunts an escaped convict who was broken out of prison by criminals using stolen military weapons; Chris prepares for a difficult goodbye when her former K-9 partner becomes ill.

Street is caught between his duty to SWAT and his commitment to his foster brother, Nate when Nate is ensnared in a criminal enterprise that could ruin them both. Also, the SWAT team goes after a ruthless crew that uses deadly force while stealing from card casinos, and Buck approaches Deacon to partner on a private security opportunity.

The SWAT team pursues a couple reminiscent of Bonnie and Clyde, when the duo goes on the run and on the hunt for a set of rare chest pieces worth millions. Also, Hondo and Darryl are surprised when Darryl’s ex-girlfriend visits with his young son, and Luca confronts his fear of failing his requalification to return to the field as he helps Kelly, his mentee.

The SWAT team goes on the hunt for a sniper who is targeting the Los Angeles Fire Department by setting fires around the city to lure in unsuspecting engine companies. Also, the rivalry between Chris, Street and Tan ratchets up when Tan finds out there’s an internal betting pool on which of them will win the SWAT leadership competition. And, Street and Molly’s relationship is strained by his complicated history with his imprisoned mother.