The most populous sprawl on earth proves a vivid barometer for the state of 21st-century civilisation in this feverish Mexico City triptych. González Iñárritu's Rottweiler of a movie slams street-level toughs up against glamorous, high society celebrity, then picks over the carnage. In the first story, lovelorn Octavio (García) turns to dogfighting to scrape enough money together to steal away his brother's wife. In the second, a magazine editor leaves his family for beautiful model Valeria (Toledo), just as an accident lands her in a wheelchair. The aftermath - involving an urban legend about a dog trapped under the floorboards - turns their lives inside out. The final story centres on an ex-Communist revolutionary (Echevarría) who prefers the companionship of mutts to people. Steeped in disgust, he accepts a contract to murder a businessman, but even as he confronts the worst, he somehow summons a shred of dignity and hope. Recalling Reservoir Dogs and Pulp Fiction - but edgier than both - this is a hell of a first film. For all its bonecrunching savagery, it's also a fundamentally moral work. The love of animals is one redeeming grace note, even as González Iñárritu makes it clear that the love of mankind is a far greater challenge.