Kate Macer (Emily Blunt) is in over her head. A tactical FBI agent with a solid record, the willingness to take the kill-shot without hesitation and no life outside work to speak of, Macer is the perfect audience stand-in in Sicario, the latest journey into the heart of darkness masterminded by Canadian director Denis Villeneuve.

Two short years ago, Villeneuve partnered us with Detective Loki (Jake Gyllenhaal) in the tense thriller Prisoners. Loki was a bit too distracted and edgy, a little off-putting for audiences to truly embrace, which might be why that story split the difference with Keller Dover (Hugh Jackman), the distressed father of one of the kidnapped girls at the center of the mystery. Dover, even in his most extreme moments, felt like someone we could ride and/or die with. Who couldn’t identity with a father pushed to the limits by a stalled search for his missing girl who simply takes matters into his own hands?

This time out, Villeneuve and screenwriter-actor Taylor Sheridan (featured roles on Veronica Mars and Sons of Anarchy obviously set up his debut foray as a writer) get the sensibility just right. Sicario drops us in the midst of an assault in the war on drugs, which has come to look — not all that surprisingly — like the war on terror. Macer and a strike force are on the hunt for a Mexican drug figure with outposts along the border, and a questionable raid leads to a brief and brutal firefight before the revelation of the real horrors lurking throughout the “secured” compound. Macer handles the situation and earns an assignment that promises to offer her the chance to do some meaningful work.

It is too bad that Macer has no real life beyond her job, because if she did, she would have realized how empty that promise was. The commander in charge of this elite unit she has been linked with, Matt Graver (Josh Brolin), shuffles into meetings with flip flops and a beach-bum demeanor, but he’s shadowed by Alejandro (Benicio Del Toro), a mysterious associate known by most of the drug world insiders who is given a wide berth by the Delta Team members, the guys ordered to kill who do so without question or qualm.

Macer can’t help asking questions, though. She’s searching for answers, for truth, for resolution. She believes, naively, that all wars must have a beginning and, more importantly, an end. She wants to know what the goals are and how close we might be to the end.

And so do we, but it becomes painfully obvious that there are no answers to be found. There will never be an end to this dirty business, just more dirt — more darkness on the horizon.

Sicario starts to feel like the bastard child of Traffic and No Country for Old Men, although it makes no attempt to fracture its perspective like the former and it cares nothing at all for the literary metaphors of the latter film. Villeneuve and Sheridan have concocted a ruthlessly simple tale, relentless in its forward movement.

And there’s a deliciously straightforward twist in the telling. We’re saddled with Macer, the assumption being that this is her story, but the truth is right there in the title. A sicario is a hitman, we are told, via an introductory title card. The film doesn’t exert much effort hiding the identity of its killer, but what it does so well, in fact, is slowly bring him into focus.

The world is full of evil; we recognize the sad truth in that statement, and we place our belief in the idea that we empower people to combat that evil. What we don’t always want to admit though is that sometimes we must enlist and unleash necessary evils to serve the greater good. The question, then, becomes: Is the greater good somehow compromised beyond recognition by its association with these necessary forces?

Maybe. Maybe not. Sicario transforms into an examination of a devil we get to know, one that probably didn’t even start out as an angel in the first place. So, in reality, he’s not a fallen figure at all. This devil was always nothing but a bad seed, but for the moment, he’s on our side. By the end, Macer certainly finds herself second-guessing the morality of such alliances. Villeneuve dares us to consider our own feelings about this situation. (Opens wide Friday) (R) Grade: A- (tt stern-enzi)