Close encounters: "Monsters"

Impossible to bracket Gareth Edwards' indie discovery Monsters. Creature feature? Philosophical road movie? Love story? Gap year travelogue? Screwball comedy along It Happened One Night lines? Best, perhaps, to acknowledge it has elements of all these diverse forms in its DNA, and to call it for the immensely fresh and vital hybrid it is: one of the most assured debuts in recent history, no less. Its backstory may be the most standard thing about it. A NASA probe has crashed in northern Mexico, spilling its cargo of squid-like alien lifeforms; the US authorities, as is their wont, have contained the area, labelled it the Infected Zone, and began bombing these extraterrestrial tourists into submission.

Our human heroes are two youngish Americans at large on what's apparently the wrong side of the border, in South America: Andrew (Scoot McNairy), a rodenty, once-divorced and thus mildly jaded photojournalist, and Sam (Whitney Able), his boss's blonde daughter, engaged to another back home but still evidently under the thumb of her controlling papa. Trying to get back to the States, they miss the ferry that would have provided them with an easy route home, and are obliged instead to travel through the Zone on foot, with planes and tentacles strafing down from above at occasional intervals, and only one another to rely upon.

If you can't pin down what Monsters is so easily, you can see exactly where it might have came from. We can assume Master Edwards has, at some point, in his young life, slept through a wake-up call in his hotel or hostel and, in the resultant panic, missed an important connection; his debut is infused from first to last with a sense of what it is to be a stranger in a strange land, a million miles away from home - to be an alien, in other words, which is where the film pulls its conceptual masterstroke, for just as we can't quite define the film, so too its very language proves fluid.

You'd have thought the title would refer to the giant octopodi stomping everything, but a graffito glimpsed during a peace demo the two leads attend on their travels instead equates the term to those carrying out the bombing. It is, then, a sci-fi movie (if it is just that) that seeks to draw no distinction between us and them, and indeed the aliens throughout come only to mirror the actions of their hosts: those being bombed understandably get aggressive, alien flora comes to reflect back the photojournalist's torchlight. Edwards shot on the hoof around unfamiliar locations in Guatemala and Belize, then did all the effects at home on his laptop - keeping it real, as it were - and it's this freshness, in conception and execution, that gets to you.

We've seen grounded SF movies before - most recently, in the firmly street-level Cloverfield and the slum-bound District 9 - but they've had to be dressed up with differing forms of gimmickry, engineered in viral-marketing labs. Monsters really is, at heart, no more and no less than the story of a girl and a guy getting to know one another, and those around them; if we were to strike off one of that opening barrage of generic tags, it would surely have to be "creature feature", because - above all else - this is an exceptionally human film, the effects forever ceding to sleepovers and chats with fellow travellers, the direction and performers trying to find ways of turning sad or despairing conversations or situations on their heads. In both form and content, the film makes the very best of things, and is thus the very best of company.

This conviviality is a shade different to that expressed by the partygoers of Cloverfield, in that it's personal; so personal, in fact, that the leads have since married in real-life and have a baby on the way. Monsters benefits hugely from the fact we haven't seen much of these players before - we're getting to know them, just as the characters come to find out about each other. McNairy, as in 2008's In Search of a Midnight Kiss, is very good at suggesting some small kernel of conscience and decency tucked away behind his surface cynicism and six-day stubble - that, in this instance, his Andrew might, some day, come to pack his lenses away and actually participate in the world, rather than merely spectate (a major failing of the cameraphone-touting Cloverfield kids, who treated the end of the world as the raw material for some spectacular YouTube footage); no spoilt heiress, Able is also winning indeed as the kind of gal for whom you'd happily run down to the port in your boxers.

In collaboration with their director, the actors give Monsters the air of real exploration, of a shared adventure - one away from the predictable avenues of the modern urban landscape, Edwards subtly insinuating there might well be something of note (and at stake) in every spot on our planet; you quickly sense the writer-director made his lead character a photojournalist just so he'd have an excuse to turn his own camera upon anything that struck him en route. So much sci-fi displays a notable fear of reality - partly, no doubt, because it's both cooked up and consumed by men shut away for large stretches of time in tiny rooms. Despite the modest means at Edwards' disposal, Monsters forms instead a loud and bold encouragement to get out there, and that we have nothing to fear but fear itself; it's a work underpinned by a young filmmaker's growing fascination with the world, and a touching faith in the kindness of others. As the finale - a properly widescreen, 21st century update of E.T. and Elliot touching base in Spielbergland, and perhaps the most transcendent happening ever witnessed on a garage forecourt - only goes to underline, we're at our best as humans whenever we try to reach out and connect.

Monsters opens in selected cinemas from Friday.