Brian Taylor and Mike Zavala are close friends and partners in the Newton Division of the Los Angeles Police Department (LAPD) in South Central Los Angeles. Taylor, a US Marine veteran, is recording their police activities for a film project.
Upon responding to a public disturbance call, Tre, a Bloods gang member, yells racial insults at Zavala, who responds by accepting a one-on-one fist fight. Zavala beats and arrests him, but wins Tre’s respect for not charging him with assault. Later that night, Tre and his fellow Bloods gang members are attacked by a group of Sureños in a drive-by shooting and one of Tre’s friends is killed. The next day, the officers respond to a noise complaint at a house party full of Sureños, where Taylor and Zavala encounter gang members named Big Evil and LaLa.
Taylor and Zavala are awarded the Medal of Valor after rescuing three children from a house fire. Upon further investigating a house, they arrest a man who is also in possession of several ornate firearms, and is guarding a cell full of human trafficking victims. When ICE officers arrive, one officer informs the officers that the house is tied to the Sinaloa Cartel, and strongly urges them to “lay low” due to possible reprisals. Around this time, Taylor begins dating a woman named Janet, and Zavala’s wife Gabby gives birth to their first child.
One night, Taylor and Zavala respond to a call from their fellow officer, Sook, and find her partner Van Hauser with a knife through his eye. He leads them to Sook, who is being savagely beaten nearby. After arresting the culprit, the officers learn that Van Hauser is not returning to patrol and Sook is leaving the force. Taylor marries Janet, and at their wedding Zavala tells Taylor that, should anything happen to him, he will take care of Janet.
The next day, the officers perform a welfare check on an elderly woman. In her house, they discover drugs, dismembered corpses, and a message from the cartel. Unbeknownst to them, a cartel member has “green-lit” the officers, and the gangsters from the earlier drive-by begin following them. On patrol the officers encounter Tre who, out of respect for Zavala, warns them that the cartels plan to have them killed, but Taylor and Zavala shrug it off.
Shortly after Janet becomes pregnant, the officers are baited into chasing a reckless driver into an apartment complex, where they are ambushed by the same group of Latino gang members. They fight their way into an alley, where Taylor is shot in the chest. As Zavala desperately attends to his partner, the assassins arrive and shoot him several times in the back. Police backup eventually arrives and the gangsters are killed after refusing to surrender.
Taylor survives, having been shielded by Zavala’s body. At Zavala’s funeral, Taylor tries to deliver a eulogy, but only manages to say a few words: “He was my brother.” In a flashback to the day of the shooting, Zavala recounts to Taylor a story from his teens before the two receive the call from dispatch.