Denis Villeneuve’s latest film, Sicario, opens on the outskirts of Arizona, where FBI agent Kate Macer (Emily Blunt) and her team invade a house in the hopes of finding hostages. Upon some investigation, they discover dozens of rotting, naked corpses stored within the building’s walls. It’s a deeply disturbing sequence and acts as a potent visualization of Sicario’s overall thesis: scratch beneath the surface of evil, and even more heinous, pungent evil awaits you.

The corpses turn out to be victims of drug cartels. This inadvertent exhumation brings Macer to the eye of Matt Graver (Josh Brolin), a CIA agent and Dept. of Justice consultant who leads top-level missions on the US-Mexican border to fight the War on Drugs. From the minute we see Brolin with his goatee and flip-flops, it’s obvious that he’s the type of guy to describe himself as “not playing by the book.” What isn’t obvious right away, to us or Macer, is why he needs her to accompany his mission.

As an actress, Blunt has always shown a keen eye for determining the tone of the project she is in. Whether an acerbic comedy with a heart of gold (The Devil Wears Prada), an attempt at lightly raunchy romantic comedy (The Five Year Engagement) or an action film with a brain beneath the metal (Edge of Tomorrow), Blunt consistently excels at delivering complex performances that draw out the best in her co-stars and help articulate the films’ themes. Here, she is saddled with an especially tricky balancing act, and Villeneuve and company could not have chosen a better actress for the job. Her character is, quite literally, a plot point; multiple times throughout the movie’s duration she is told that she is only there so the mission can be carried out without any eyebrows raised from higher command. Her presence grants Graver and his crew legitimacy. Not much more is expected from her than to watch. Macer’s role in the film as a whole is similarly limited. She is meant as a conduit for the viewers, a person similarly foreign to this system of high-reaching intrigue and corruption who will be alarmed, baffled, and morally outraged alongside the audience.

Blunt certainly fulfills both of these tasks, but does something much more difficult at the same time. She smartly invests her character – through hunched posture, and knowing but bleary eyes – with a sense of resignation to the evils of the world from the opening of the film. It’s this lack of naivete that makes her eventual astonishment at the extent of the corruption within the upper levels of the “war on drugs” pack the emotional punch it does.

Oddly less affecting is Benicio del Toro’s turn as Alejandro, an eminent CIA agent with mysterious origins and priorities. Del Toro is excellent at playing a man who lives in the shadows, carrying out deeds others know better than to ask about. However, the film somewhat overplays its hand by sprinkling in copious suggestions that he is a man who has had bad things—whatever those may be—done to him and, as a result, will be willing to do equally bad things to right those wrongs. Consequently, when Alejandro gets the chance to do said bad things, it’s a little bit hard to be as appalled as the film, by framing it as one of its hand-to-mouth dramatic climaxes, indicates it would like us to be.

The rest of the cast and crew all excel. Brolin uses his raffishness to convey something much more toxic beneath the surface, and Victor Garber is reliably terrific as an official who understands how little power he really holds. It’s no surprise that cinematographer Roger Deakins stands out, but his sterile yet stunning aerial views of Mexican towns and Texan deserts, as well as a sequence shot entirely in heat-vision, deserve a special place even in a storied filmography like his. A more novel presence is Icelandic composer Jóhann Jóhannsson – until now best known for an appropriately mawkish score for The Theory of Everything – whose score resurfaces at unexpected points to provide the film with a pulsating, ominous sonic backdrop.

Overall, Sicario, like Blunt, manages a difficult balance by not directly indicting the crooked world it presents, but showing the all-too-human tolls it reaps as well. In doing so, its border setting acts as a suitable metaphor: the War on Drugs transgresses boundaries not only physical but also moral, and the audience feels the weight of these transgressions with every passing minute.