This debut feature by Cary Fukunaga attempts to highlight two social problems in one film. Set in Mexico, it examines gang culture and immigration, and the ways that they affect the youths of South America.

Casper (Édgar Flores), despite being relatively young himself, has been a member of the Mara gang for some time. Smiley (Kristian Ferrer) isn’t even in his teens, but is drawn to the so-called glamour of being in a gang. Casper acts almost like a mentor to young Smiley, as he guides him through the traumatic initiation tests that, if he passes, will see him as a member for life.

Meanwhile, Sayra (Paulina Gaitan) is making a treacherous journey by train from Honduras to North America, with her father and uncle. They, like so many, risk their lives on this trip, in order to have a better life.

Casper finds himself distracted from his gang duties by his beautiful girlfriend, who he’s keeping a secret from his gang – with good reason. When these two very different worlds clash, it ends in tragic consequences.

When his gang leader makes Casper and Smiley join him on an outing – which finds the trio robbing poor immigrants on the same train Sayra and her family are on – two worlds collide again, albeit different ones, with yet even more tragedy to follow. The result of which finds Casper and Sayra on the run from both the immigration police and, more worryingly, the Mara gang who don’t like to be crossed, especially by one of their own.

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With echoes of 2002’s City of God, Fukunaga beautifully weaves two seemingly disparate storylines into one. The gangs of Mexico appear to be even less fun than those of Brazil, particularly when you take into consideration that the initiation process includes murder.

Fukunaga paints his vision on a canvas of hopelessness. Flores does a fine job in evoking a heady air of desperation in Casper; the character feels like he’s living on borrowed time as it is, which he conveys remarkably with his physical demeanour.

And despite an almost too instant attraction from Sayra to Casper when they first meet, their relationship does become one that you could see developing with a certain degree of realism.

The director is also lucky to get a great performance from the young Ferrer, whose Smiley has to mentally process a huge amount of conflicting emotions regarding friendship and loyalty.

Acting almost as a third wheel, the audience becomes like a silent passenger on this journey fraught with danger. We may not always like the direction we’re being taken, but that’s only because we’ve invested a relationship of our own with the runaway couple.

There are probably equal moments of bleakness and beauty in this film; they have to remain hand in hand as to maintain its real sense of earthiness. It’s by no means an easy ride, but it doesn’t stop it from being any less compelling.