With Donald Trump’s controversial "zero tolerance" immigration policy keeping the US-Mexican border in the headlines, the timing couldn’t be better for this sequel to the lauded 2015 thriller concerning more covert aspects of America’s battle with the Mexican drug cartels.

Emily Blunt and director Denis Villeneuve are the notable absentees from the original. But the formidable Josh Brolin and Benicio Del Toro are back as, respectively, federal agent Matt Graver – a man for whom ‘the end justifies the means’ is putting it mildly – and his go-to freelance operative, the mysterious lawyer turned assassin Alejandro.

Following a harrowingly depicted suicide bombing in Kansas, Graver discovers that one of the terrorists was smuggled into America from Mexico. The agent is called before the secretary of defence and instructed to up the ante against the cartels, with the clear message that “dirty is exactly why you’re here”. Graver hires enough hardware to initiate a small coup, then contacts his man Alejandro. “No rules this time,” he says with a smile. “I’m going to set you loose.”

His cunning plan: to kidnap a drug kingpin’s 12-year-old daughter and make it look as though she’s been taken by a rival – setting the cartels upon each other and keeping the US out of it. The kidnap is a walk in the park; but the question of what to do with the frightened girl (Isabela Moner) once they have her causes the operation to go belly up. And suddenly the two amigos Matt and Alejandro find themselves pitted against each other.

The film is again scripted by Taylor Sheridan, who doesn’t do half as well this time. The plotting around Graver’s stuttering masterplan is horribly muddled, there’s so much toing and froing across the border that it’s easy to forget which country you’re in, and the speed with which this fictional US administration loses its nerve simply doesn’t wash.

The moral maze was also more tightly wound last time around, particularly since it had Blunt’s idealistic FBI agent to question her unscrupulous colleagues.

Compared to the original, this feels routine; but alongside most other crime thrillers, it’s still a cut above. Directed by the Italian Stefano Solima, whose credits include the TV series Gomorrah, it retains the pulsating intensity and sense of doom around every corner, the rightly pessimistic depiction of individuals and communities wholly messed up by endemic crime, and the thought-provoking blur between good guys and bad – it realty is difficult to know what to make of Graver, in particular, who Brolin imbues with both righteousness and relish.

While Solima orchestrates some extremely exciting set pieces, notably a brutal gun battle between soldiers and police, the chief interest is in the way that Brolin and Del Toro have developed their characters from the previous film and, surprisingly, given each of them a little more light.

Graver may take too much pleasure from an interrogation, telling his prisoner that “waterboarding is for when we can’t use torture,” but he’s genuinely challenged by a moral and personal dilemma as the film reaches its climax, seeing the importance of the single, life-or-death consideration aside from the big picture. And Del Toro, who played Alejandro in the first film as a man emotionally cauterised by tragedy, shows him softening as he takes the girl under his wing.

The impressive Moner lends a touching combination of feistiness and vulnerability to a girl whose short life has been tainted by people’s fear of her father. Her scenes with Del Toro – damaged dad and someone else’s messed up child – are a briefly hopeful respite from the chaos.