Teenagers Julio (Lena) and Tenoch (Garcia Bernal) are falling headlong into adulthood propelled by their hormones and their heady zest for life.

Despite their differing backgrounds - Julio has been raised by his single mum while Tenoch is the privileged son of a dodgy politician - the two 'charolastras' (spiritual cowboys) are inseparable.

When their girlfriends disappear to Italy for the summer, the pair find themselves introduced to 28-year-old Luisa (Spanish actress Maribel Verdu) at a society wedding party.

They cheekily invite her to spend a few days with them camping on an idyllic beach called Heaven's Mouth - a location they made up on the spot to impress her. Luisa initially refuses but, when her obnoxious writer husband admits he's been sleeping with other women, she calls them back and accepts their offer.

So begins what might be a traditional road movie - full of sex and drugs - but also an intelligent and humorous look at male machismo and how it wilts when faced with a strong woman. In turn, the boys are seduced by the older woman, who makes it pretty clear she isn't impressed with their prowess.

The strange threesome's emotions swing back and forth from jealousy to joy as the group dynamic is contorted by the wilful Luisa and the increasingly strained friendship between Tenoch and Julio. A brusque voiceover also puts their passage in context, painting in the general malaise of a Mexican society riddled with corruption and government brutality.

Luna and Bernal give very natural, gauche performances while Verdu provides the sensual maturity, veering from kitten to fox. To repressed British viewers the sex scenes may cause a bit of a stir - but only in that they are achingly realistic in a Latin manner you never see over here.

Director Cuaron rarely puts a foot wrong in putting together a successful rites of passage road movie while putting the boot into the male sexual bravado of his own country.

Natalie Stone