A locally born SWAT sergeant, former Marine Daniel “Hondo” Harrelson, is newly tasked to run a specialized tactical unit that is the last stop in law enforcement in Los Angeles.

After a domestic bomber dies in a Highland Park explosion, the SWAT team races to find the man's partner before more devices detonate. Also, Hondo reaches out to Buck, his former team leader, when he worries he is isolating himself after his recent firing.

Hondo and the team go on the hunt for a serial killer who escaped justice two years prior by faking his death. Also, Hondo worries that Buck Spivey, the team’s former leader, is spiraling into depression in the aftermath of being fired from the department.

The SWAT team faces difficult reminders of a past school shooting when they receive a warning that a copycat plans to re-enact the crime. As the team races to stop the new threat, they flash back to the day of the tense first mission.

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.

Deacon’s second job working private security at a high-profile boxing match places the SWAT team in the middle of a kidnapping case when a prize fighter’s wife is abducted. Also, Hondo’s young charge, Darryl, becomes frustrated with his lack of paternal rights regarding his infant son, and Tan prepares to introduce his critical mother to his girlfriend, Bonnie.

The SWAT team must protect a hotel full of civilians after a joint task force mission with the LAPD Gang Division goes wrong, and the city’s most dangerous gang leaders scatter across the building to find an escape. Also, Luca’s efforts to coordinate the team’s mission are complicated when his brother, Terry, a freelance stringer reporter, crosses police lines to shoot footage.

Hondo and the SWAT team race to save Buck, their former unit leader, when he goes off grid and they fear he plans to harm himself. Flashbacks reveal the search for Buck, which coincides with one of the team’s most brutal missions, as each team member receives counseling and discusses the untold mental and emotional difficulties inherent to working in SWAT.

Tan finds himself on a one-man mission to save his new love interest and her journalist co-workers when mercenaries take over a black-tie correspondents' dinner. After the group escapes, it's up to SWAT to track down the well-trained gunmen.