Plot summary

The film opens with a high-speed police pursuit ending in a shooting in South Central Los Angeles. The officers involved, Brian Taylor (Jake Gyllenhaal) and Miguel Zavala (Michael Peria), are close friends and partners in the LAPD. Taylor, a former Marine, is filming their police activities for a film project, much to his fellow officers' chagrin.Later, the officers respond to a public disturbance call. The culprit, a Bloods gang member named Tre, hurls racist insults at Zavala, who responds by accepting a fight, to Taylor's approval. Zavala beats and arrests him but wins the man's respect for not charging him with assault. Later that night, Tre and his fellow Bloods gang members are attacked by a group of Surenos (Southerners) in a drive-by and one of Tre's friends is killed. The next day, the officers find the burnt vehicle used in the drive-by and are shooed off the scene by homicide detectives.The officers later respond to a missing children call, only to find the home to be a crack house with the children duct-taped in a closet. Later that night, the officers respond to a noise complaint at a house party full of the Latino gang members, where Taylor encounters a gang member named Big Evil. Big Evil & his gang members had carried out the drive by shooting on Tre's gang. Taylor begins dating a woman named Janet (Anna Kendrick). Taylor has a hunch and decides to scope out the home of the mother of Big Evil. The officers follow and pull over a truck that leaves the house - the driver draws a gun and is arrested. Inside the truck they find ornately decorated firearms and a large amount of money.Days later, the two officers rescue some children from a house fire but come out barely alive. The two are commended and receive the Medal of Valor. Using the house fire incident as leverage, Taylor convinces Zavala to further investigate the house involved in the incident. At the house, they arrest another man, who is also in possession of several ornate firearms, and is guarding a cell full of human trafficking victims. Suddenly, ICE agents arrive and take over the scene. One agent informs Taylor and Zavala that the house is tied to the Sinaloa Cartel, and strongly urges them to "lay low" due to possible reprisals.Zavala's wife Gabby (Natalie Matrinez) gives birth to the couple's first child. One night, the two receive an 'officer needs help' call from Sook, Van Hauser's probationary partner. Urgently responding to the call, the two find Van Hauser on the ground, alive but with a knife through his eye. He points them to a nearby alley, where they find Sook being savagely beaten by a large Latino gang member. Taylor chooses to arrest the attacker instead of killing him. As the victims are carried away by ambulance, the officers discover that Van Hauser is not returning to patrol, and Sook is leaving the force.Taylor marries Janet. At the wedding, Taylor and Zavala's boss, "Sarge," drunkenly recounts a story to three Marines about his dead partner, who took a bullet to save him. Afterward, 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 at request of her daughter. After receiving no response at the door, the officers break in and discover drugs, dismembered corpses and a message from the cartel.Elsewhere, ICE records surveillance footage in Mexico of a cartel member putting a contract killing on the officers. The gangsters from the earlier drive-by begin following the officers, plotting their assassination. Out of respect for the incident between him and Zavala, Tre warns Taylor and Zavala of rumors that they have been "Green lit", but they disregard his comments. Janet becomes pregnant shortly after the marriage. One night, 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. Taylor is shot in the hand, and his radio is destroyed. Taking refuge in an apartment, Taylor decides that they are going to have to gun their way out. The two fight their way into an alley, where they are fired upon again. Taylor is shot in the chest and appears to die. As Zavala desperately attends to his partner, the assassins arrive and shoot him several times in the back, killing him. Backup eventually arrives and the gangsters are also killed after refusing to surrender.At the police funeral, it is revealed Taylor survived, because Zavala's body had shielded him from the gangsters' gunfire. He tries to deliver a eulogy, but only manages a few words: "He was my brother".The last scene shows the two officers on the day of the shooting, where Zavala tells a funny story where when he was younger, he was about to be intimate with Gabby, but her parents unexpectedly came home. He had to hide under her parents' bed and listen to them have sex. The two then receive a call from dispatch and cheerfully head off to "Fight crime."