When a strange and unclassifiable beast walks into the world, the public has a tendency to split down the middle. One camp is beguiled and the other repulsed. Such is the experience of the vampiric space alien played by Scarlett Johansson in Under the Skin, and so it is with the film itself. Jonathan Glazer's extraordinary piece of outsider art – the director's first feature since 2004's Birth – was greeted at Venice by an even split of cheering and boos.  A pox on the cat-callers; they can boo themselves hoarse. Under the Skin is far and away the best picture in the competition so far: a story that plays as a kind of malarial dream, bathed in cold sweat and seeing hallucinations in every corner. Johansson proves bizarrely engrossing as the unnamed succubus, fetchingly augmented with jet-black hair and blood-red lipstick, who drives a van around Scotland in search of her prey. The men she meets are bored and horny and can't believe their good fortune. The alien duly lures them in with polite, persistent questions, barely pausing to hear the replies. Then she ushers each man down the steps into a pool of viscid fluid where they spot the bodies of former victims, floating naked in the gloom like Bluebeard's wives.  We are never told where this alien is from or what she's doing, exactly, although the film takes its lead from a 2001 novel by Michel Faber. Slice it open and one realises that Under the Skin is actually a hybrid of two hackneyed film genres. It's indebted on the one side to the psychosexual horror movie in which feckless, lusty youths receive their comeuppance and, on the other, to those fish-out-of-water capers (like ET, or even Splash) about kooky visitors from the wide blue yonder. And yet the director works a magic on this material. He takes tired old prose and spins it into poetry.  In a perfect world, Glazer would win the top prize on Sunday and not have to wait another nine years before he makes his next film. But we do not live in a perfect world, and Under the Skin is perhaps best viewed as an icy parable of love, sex and loneliness. The director leads us between empty seashores and cacophonous nightclubs. He turns a hidden camera on the streets of Scotland and watches unnoticed as the people shop and smoke and tap out their texts.  Increasingly, it seems, Johansson wants to find a place in this throng. But try as she might, she can't quite fit. The TV set is a mystery, and the slice of chocolate cake only sticks in her throat. Driving on the road, she encounters a fellow pariah, a young man with a bone deformity, who shops by night and has no friends. A little later we shall see this figure again, wandering naked and bewildered on the outskirts of town, just another lost soul who's in search of a home.  • Exclusive video of Under the Skin  • Under the Skin heads triple bill of long-awaited films
A sexy space alien hunts men in Scotland in this extraordinary malarial dream from Jonathan Glazer, writes Xan Brooks