Denis Villeneuve’s “Prisoners” was an engrossing kidnapping drama that also spoke volumes about the darker elements of human nature when a victim’s father chose to take matters into his own hands. A similar pattern applies to “Sicario,” an enthralling treatment of the war on the drug trade which also implicitly analyzes that policy in a way some will see as stinging and others as cynical. It’s a brilliant, unsettling piece of filmmaking.

The viewer’s surrogate is Kate Macer (Emily Blunt), a young FBI agent in charge of a kidnapping squad. In a set-piece early on, she and her partner Reggie (Daniel Kaluuya) lead a SWAT-style assault on an Arizona drug house, where dozens of corpses are found rotting behind the walls. The success of the raid, despite a major setback during the search of the property, leads her chief Jennings (Victor Garber) to allow Matt Graver (Josh Brolin), a gregarious but mysterious agent, to add her to a unit he’s putting together for a special mission. Among its other members is Alejandro (Benicio Del Toro), an even more mysterious but far quieter Colombian who will turn out to be the sicario—a term, we’re told, for “hitman”—of the title.

The first part of the mission turns out to involve the extraction of a member of the Diaz cartel from the custody of Mexican officials in Juarez, a city that’s an epicenter of drug-related violence. It ends with a tense confrontation at the border crossing—a remarkable piece of action choreography that paradoxically involves vehicles that are stalled in traffic rather than the speeding ones that would ordinarily be the focus of such a scene. The “enhanced” interrogation of the subject in turn leads to a couple of further strikes on the cartel—one to disrupt its money-laundering and the other to interrupt the delivery of product through a tunnel across the border. They’re designed to rattle the head Diaz honcho in US territory to send him scurrying for a sit-down with the hitherto unknown cartel head in Mexico—giving the Americans a chance to tail him to his destination.

The script concocted by Taylor Sheridan isn’t really excessively convoluted, but he and Villeneuve play fair with the audience, doling out information in bits and piece so that we learn the truth about what’s happening just as Kate does (and, it must be added, viewers don’t have to undergo the physical punishment the heroine suffers along the way, some of it very severe). Some of the revelations involve the role in events played by a Mexican policeman (Maximiliano Hernandez) whom we meet early on in scenes with his soccer-playing son, and who reappears periodically, eventually becoming a major figure in the action.

Blunt anchors the film with an intense performance as a woman trapped in a situation that she can’t fully understand and that makes her increasingly uneasy as she pieces together how she’s being used, and truly unnerved by the time she realizes what the whole operation has actually been designed to achieve—an emotional arc the audience will experience with her. Brolin strikes the right air of nonchalantly devil-may-care ruthlessness, while Kaluuya provides a measure of authentic camaraderie and the others (Garber, Hernandez) help to increase the uncertainty about motives and morality that drives the plot. Bernardo Saracino and Julio Cesar Cedillo appear in the closing reel, with the latter delivering an impressively powerful few minutes of screen time.

Despite the overall level of excellence among the cast, however, it’s Del Toro who ultimately drives the action with a turn that fascinates from his first appearance and never lets up until the very end. Exhibiting a quiet, world-weary attitude that can turn on a dime to seething determination, Del Toro manages to humanize Alejandro with just a few minimal gestures while keeping the audience constantly in suspense about his next move. It’s as mesmerizing a performance as the one he gave on the other side of things recently as drug lord Pablo Escobar in “Paradise Lost.”

“Sicario” boasts striking cinematography by Roger Deakins, with scenes of the desolate borderlines shot from above, the tiny shadow of a plane snaking across the landscape, that contrast sharply with the outdoor sequences of dense urban sprawl and interiors that, even when large and elegant, convey a feeling of confinement. He and editor Joe Walker work with Villeneuve to craft a few remarkable set-pieces—that border-crossing confrontation in stalled traffic, the assault on the drug-runner’s tunnel, and the final face-off in Mexico among them. Johan Johannsson adds to the mood with a score that drones and growls but adds propulsion as needed. Patrice Vermetter’s production design, Paul Kelly and Bjarne Sletteland’s art direction, Ricardo Guillermo’s set design, Jan Pascale’s set decoration and Renee April’s costumes all contribute unobtrusively to the overall effect.

Despite its high voltage, “Sicario” is hardly a typical Hollywood action film. Unrelentingly tense and unremittingly grim in the portrait it paints of both sides in the so-called war on drugs, this is a film that challenges convention just as “Prisoners” did. Villeneuve has made another film that’s adult in the best sense.