In David Ayer’s “End of Watch," Brian Taylor (Jake Gyllenhall) and Mike Zavala (Michael Peña) star as two LAPD officers who unknowingly disrupt a drug cartel’s operations.

Usually, the sound of bullets hitting their target is only followed by a fist-bump if the bullets were fired by a video game controller and if the player is not alone in their basement. Not so in the opening of David Ayer’s “End of Watch,” as LAPD officers Brian Taylor (Jake Gyllenhaal) and Mike Zavala (Michael Peña) quickly gun down two men after a lengthy car chase shown from their point of view.

“End of Watch” follows Taylor and Zavala’s increasingly dire straits as they unknowingly disrupt a drug cartel’s operations in southern Los Angeles and are targeted by heavily-armed pushers. The compelling, occasionally nerve-wracking plot and simple, effective staging combine to create a gripping story of two policemen being continually beaten to the ground—both physically and mentally—and a moving depiction of friendship by Gyllenhaal and Peña.

Initially, neither Taylor nor Zavala are very likable characters. Respectful policemen, after all, are not expected to pound fists after killing two men, nor are they supposed to display their weapons to the camera the way little girls show off their Barbies. At first, their only apparent redeeming quality is their jovial, sometimes crass, and incredibly dedicated partnership.

However, as the loose camera continues to follow Taylor and Zavala while they respond to emergency calls and investigate various strange noises emanating from suspicious houses, the lightheartedness that seemed insensitive earlier is revealed as a necessary way for the two men to cope with their job. As they encounter increasingly horrific and gruesome crimes—Ayer sparing no detail as knife wounds and dismembered bodies are shown up close—it is clear that if the officers allowed themselves to wallow in uncertainty or guilt, they would be unable to carry out their day-to-day business.

The short glimpses of the emotional aftermath feel genuine and harrowing, thanks to Gyllenhaal and Peña’s unforced, nuanced performances. After making an arrest in a particularly disturbing case, Gyllenhaal can communicate the toll being taken on him in merely the slump of his shoulders and a slight headshake. Zavala reacts differently, staring blankly at a crime scene as if he’s not quite sure if he believes what he’s seeing. Later, after both officers receive medals for their courage, Taylor hesitantly and endearingly asks Zavala, “Do you feel like a hero? What does a hero feel like?”

At times, “End of Watch” inflicts similar distress upon its audience: the pacing of the film can pack so much intensity and violence into certain segments that the overwhelming tension takes away from the story itself. Some confusion and inconsistency is apparent as the found-footage styling, justified by a film project Taylor is working on for pre-law courses, is occasionally switched out for typical third-person camerawork and footage mysteriously attained from the cartel’s members.

Gyllenhaal and Peña’s easy, bantering depiction of a profound relationship quickly compensates for the erratic camerawork, as Taylor begins dating Janet (a sweet but forgettable Anna Kendrick) and Zavala celebrates the birth of a son. The two discuss all of this, both seriously and jokingly, in the front of their police cruiser, which begins to seem like the only place where they both can truly relax.

Quite a bit of the film is committed to Taylor and Zavala’s banter within the car, so the staging of “End of Watch” is not always very dynamic. But when there is a change of setting, it is usually made striking through simple details: a fluttering plastic sheet over a door in a suspicious house, smoke wafting slowly out of a suspect’s mouth during a confrontation, or the unsettling sight of uniformed policemen sprinting down an alleyway, screaming for help.

In the end, though, the film relies on its actors as much as the characters they play rely on each other. Ayer, perhaps aware of this, concludes “End of Watch” not with a deep reflection on the bloody and trying events that transpired or with a dramatic monologue to match Taylor’s opening voice-over, but on an everyday conversation between Taylor and Zavala—a tribute to the strength required not to fire a gun but go back to work the next day, and to the devoted bond that makes it bearable to do so.

—Staff writer Natalie T. Chang can be reached at nataliechang@college.harvard.edu.