Officers Brian Taylor (Jake Gyllenhaal) and Mike Zavala (Michael Peña) are partners patrolling South Central Los Angeles. It's a day-in-day-out routine of protecting and serving, mundane enough by cop standards (meaning there's an ever-present threat of real violence and danger that would unnerve civilians, worn lightly by the men in uniform) that Taylor feels comfortable attaching himself to a small camera, documenting his working life for a film class. Nothing especially plot-driven goes down, nobody's moving toward a big bust or enveloped in a looming crime wave. Or so they think.
They have domestic lives, too. Zavala's pregnant wife (Natalie Martinez) and Taylor's new girlfriend (Anna Kendrick) emerge from the usual action-movie "woman" sidelines and provide -- whether they're onscreen or off -- an added dimension to the suspense felt every time the officers run up against the story's slowly revealed threat: intense brutality in the form of Mexican drug cartels, now operating quietly in Los Angeles. Shoved out of the way by FBI every time they sneak a peak at the human trafficking, mass graves and evidence of torture that embodies cartel mayhem, Taylor and Zavala find themselves locked into fighting an overwhelming force they haven't been allowed to see coming.
Playing down the main event until it's too late for the characters to respond adequately is a narrative gamble. Tough-Guy Movies usually take the easier road, the one where action trumps whatever else the first draft thought it might try to accomplish before the Tough Guys find a way to crush the evil. But this time around the Tough Guys are people. And they spend a lot of time becoming characters. That's something usually flushed away by directors more concerned with how the guns fire than how the gun-firers talk to one another. Writer/director David Ayer's most well-known script, Training Day, followed a familiar Tough Guy Movie path and, despite its rough energy, its constant alpha posturing overwhelmed its humanity.
But as Taylor and Zavala, Gyllenhaal and Peña share an ease and brotherly chemistry that keeps their characters from feeling like cop "performance" even though they're constantly the objects of a self-imposed camera. Their cumulative effect more resembles actual friendship as they joke, live their lives, find themselves challenged by other cops (America Ferrera shows up in a small role as a dismissive female officer) or face the damage imposed by their dangerous work. As the consequences of their patrol routine become more clear and more frightening, you'll be moved in a way that a film that's all blammo can't deliver.
So if, in the end, it still doesn't have much to say about the nature of police work or crime (its cartel men and local gangstas are laughable, Scarface-level profanity-spewing stereotypes, more like walking, talking "homies" action figures than anything else) and if it refuses to take menace to its most logical conclusion, it's still smart about the way men bond through constant proximity and violence, a suspenseful and solidly entertaining buddy-cop drama, like Training Day with its heart on its sleeve.