Emily Blunt delivers a brilliant performance as a straight-arrow FBI agent whose eyes are opened to the murky realities of the war on drugs.

In this queasily gripping thriller from director Denis Villeneuve, she’s recruited to a secret government task force led by Josh Brolin’s deceptively laid-back, flip-flop-wearing agent.

As the team criss-crosses the US-Mexico border in the hunt for an elusive drug cartel kingpin, blurring ethical lines as they go, Blunt’s character provides the film’s moral compass and the audience’s viewpoint.

Along the way, there is a brutally tense ambush at the Juarez/El Paso border crossing and a chilling nocturnal raid on a tunnel beneath the border, strikingly filmed using night vision and thermal imaging cameras.

These standout scenes pack a punch, but it’s the film’s pervading sense of dread and unease – enhanced by Roger Deakins’ sublime cinematography and Jóhan Jóhansson’s skin-prickling score – that keeps us on edge throughout, as does the presence of Benicio Del Toro’s troublingly enigmatic advisor, the mysterious foil to Blunt’s doggedly upright, yet all too vulnerable, heroine.