People with high blood pressure should stay far, far away from Sicario.

This is an exercise in prolonged tension like few others. Every moment from the first scene to the last is suspenseful. The opening, a deadly raid on a drug kingpin’s safe house establishes a terrifying precedent: In this film, violence can erupt at any time without any warning, and no one and nothing can be trusted. Having thoroughly unsettled the audience, director Denis Villeneuve keeps viewers on edge with shifty characters, sudden bursts of gunfire, and the careful use of a persistent, pounding score. Remember the scene in Boogie Nights where Alfred Molina is randomly tossing firecrackers at Mark Wahlberg and John C. Reilly? Sicario is like that scene for two straight hours with no “Sister Christian.” It is intense.

It is also a tale of the war on drugs — with a heavy emphasis on the “war” part, and the morally and ethically questionable actions of the U.S. military and the CIA, who (at least in this film) operate on both sides of the U.S.-Mexico border with little oversight or consideration of due process. Our entry point into this world is FBI Agent Kate Macer (Emily Blunt), a skilled member of a tactical unit specializing in kidnappings. After a brutal opening scene set in the midst of a drug raid, Macer’s reassigned (or, more accurately, forcefully volunteered) to a drug task force given extraordinary power to “shake the tree and create chaos” for a Mexican drug cartel. Her new co-workers include gregarious, care-free Matt (Josh Brolin), and stoic, solemn Alejandro (Benicio Del Toro). They claim they’re headed to El Paso; they are not. They claim they work for the Department of Defense; they don’t.

Kate has never been to Juarez and has no experience with the world of cartels, so she’s the ideal protagonist for a film like Sicario, whose viewers will share her naive understanding of the drug war. She keeps asking questions on the audience’s behalf; Matt and Alejandro repeatedly deflect them, offering as little information as possible. (“You’re asking me how a watch works,” Alejandro says to Kate. “For now, just keep an eye on the time.”) Her education — and ours — is as swift as it is shocking. On her first trip to Mexico, Kate witnesses bodies, naked and decapitated, hung from overpasses, and gets trapped in a dangerous firefight when her convoy is unexpectedly caught in border-crossing traffic.

Both the script, by actor-turned-screenwriter Taylor Sheridan, and the visuals, by master cinematographer Roger Deakins, bear equal amounts of horror and poetry. At times the graphic bloody imagery is like something out of a horror film; at others, like the helicopter shots showing the disparity between the U.S. and Mexico on either side of the border, look like something out of a luminous documentary about desert topography. Later, Villeneuve and Deakins put on a clinic when they film a nighttime gun battle entirely in night vision and thermal vision. Though the story and the bleak tone recall movies like Zero Dark Thirty, Traffic, and Syriana, the film has a look and feel all its own.

It also has three outstanding lead performances. Brolin and Del Toro, playing bad cop and even-more-despicable cop, deliver Sheridan’s dialogue with relish; they’re the best performances either has given in years. And Blunt, given the difficult role of audience surrogate and frustrated, repeatedly stymied hero, cements her reputation as one of her generation’s most versatile actors. She can do romance. She can do comedy. She can do drama. She can do action. Here she has to play innocent but not dumb, tough but not cold, vulnerable but not weak, all with almost no backstory. She pulls it off.

Though the vague outlines of Matt and Alejandro’s plan are clear, the specifics rarely are. Even at its most comprehensible, there’s a lot Sicario deliberately leaves unsaid, and it builds to a crescendo of mayhem and moral rot worthy of a great film noir. The story eventually winds down, but the tension never dissipates. Villeneuve, whose direction grows more confident with each film (he previously made the so-so Prisoners and the pretty good Enemy), puts on a clinic in cinematic anxiety. Right up until the very last moment of the film, I remained convinced that any of the characters could kill each other at any moment. You never know when Villeneuve is going to toss another firework.