The specific nature of the sins committed by the citizens of Sodom and Gomorrah has been the subject of much speculation. Contending offences range from widespread sodomy and "going after strange flesh" to general inhospitality and being "impious to the Divinity". God's punishment, on the other hand, was a little less ambiguous: fire and brimstone, cities in smouldering ashes, all citizens dead, Lot's wife the final casualty; a job well done. In southern Italy, a few thousand years later, the Camorra is to Naples and the Campania region what the Cosa Nostra, the Mafia, is to Sicily: an age-old and highly complex criminal enterprise best defined as a multi-billion-dollar multinational corporation. In Matteo Garrone's fevered Gomorrah (released nationally on 14 May), the sins of the citizens of Campania and Naples are reduced to one overarching collective transgression: that of having allowed such a cancerous enterprise to flourish. So bleak is the landscape of graft and despair that Garrone depicts, it seems God's punishment in this instance has been simply to let everyone continue on amid the ruins.

Of the Biblical Gomorrah, Josephus said, "This country is then so sadly burnt up that nobody cares to come to it." Fruits still grow in the ruins, but "if you pluck them with your hands, they dissolve into smoke and ashes." In Gomorrah, nothing seems to have substance either - unless corruption itself is a kind of substance - and late in the film there is featured a box of freshly picked peaches that will meet, metaphorically at least, the fate of which Josephus speaks.

The ashes of a healthy society will be found where a corrupt one rules, and those ashes are everywhere in Gomorrah. This is a terrible place, an exhausted world, a landscape blighted by moral corrosion: public housing is in decay, life is cheap, death is everywhere. And yet, for all its compelling grimness, Gomorrah is a grand, high-energy film, filled with wonderful desperation, frighteningly raucous violence and a gripping multiple-strand narrative. It's an addictive rush, just like Goodfellas all those years ago. But Scorsese tried to show how the code works - that code of honour which, for all the thinness of its treacherous veneer, moulds and binds relationships, for better and for worse. In Gomorrah we see not so much the code as the business: the day-to-day actions and transactions; the unglamorous, tacky, low-rent grind of it all; and death so tradeable and so close. There's no moral high ground here. There's no ground at all, so to speak - a point made perhaps all too clearly when we see what's buried beneath the surface. (The Camorra has long controlled the toxic-waste-disposal industry in southern Italy, with disastrous results.)

A better reference point might be Scarface, Brian De Palma's high-camp, histrionic Miami gore-fest that has become, over the past 25 years, both a cult classic and a guilty pleasure. It is certainly the film of choice among Gomorrah's wannabe gangsters, and in one scene two young men run around a deserted building playing a childish cops-and-robbers game, complete with fake gun noises, repeating Al Pacino's crazed, coke-addled dialogue:

"Colombians, they're shit!"

"I'm Number One! I'm Tony Montana!"

There's something touching about these two fools; they're like Stoppard's Rosencrantz and Guildenstern, but without an iota of intelligence. The film, in fact, feels Shakespearean: all the characters are richly drawn and richly human; as in Shakespeare's tragedies, a "destiny unshunnable, like death" colours the texture of daily life. There, perhaps, the similarity ends, for Gomorrah contains no great tragic heroes. It's more of a brutalist-realist documentary about the numb; numbness and adrenalin are the driving force of its characters. Garrone has said that he shot the film as straightforwardly as possible, "as if I were a passer-by who happened to find myself there by chance", but this seems a little disingenuous, and his stylistic choices are clearly deliberate. In Marco Onorato's brilliant cinematography, generally only the figure in the close foreground is in focus, and those who are out of focus are often also in shadow. The psychological immediacy that results is at the same time viscerally personal and menacingly disorienting.

The fools, Marco and Ciro (Marco Macor and Ciro Petrone), whose fate will be no laughing matter, form one of the five narrative strands that weave together to make Gomorrah. Soon after their Scarface playacting, they come across a cache of weapons hidden in a barn; their fantasies can now become incarnate. One of the film's most extraordinary sequences shows them stripped to their underwear on some kind of vast coastal inlet - the misty, bleached swampiness of which might serve as a metaphor for the entire Gomorrah world - as they test out, across the watery distance, all manner of powerful weapons.

A middle-aged man, Don Ciro (Gianfelice Imparato), and a 13-year-old boy, Toto (Salvatore Abruzzese), guide the two dominant plot strands. (The film has a similar structure to the Oscar-winning, vastly overrated Crash, but that film felt like it had been made from an Ikea screenplay-construction kit, and was crippled by its artifice before being murdered by its political correctness.) The middling, efficient functionary Don Ciro does the rounds, bringing money to the families of prisoners who are part of the clan. He is quiet and courteous, almost to the point of invisibility. He's not even an accountant, though he looks and dresses like one; he's more a deliveryman. But the different clans are at war out there. Allegiances are shifting - although, naturally, "This is the right side" - and when Don Ciro gets caught in the middle his regulated world begins to fall apart. "These things are none of your affairs," he is told when he questions the wisdom of going into certain areas and asks why changes have been made to his payment schedule. "Respect the list," he is instructed.

Toto, the young boy, wants to join the big men. During a police raid he sees a man, one of the clan, throw down a pistol and a bag of drugs, which the pursuing officers don't notice. Seizing the opportunity, Toto clambers up to the spot, retrieves the gun and drugs, and later returns them to their owner. It's admirable behaviour, and he's fast-tracked into the organisation to undertake a kind of junior apprenticeship. First, in a surreal scene, he will be shot during a ritual that all new hopefuls must go through. One by one, they don a bulletproof vest and are shot at by a clan leader, the force of the impact knocking them to the floor each time. "Are you scared?" asks the shooter, when it is Toto's turn. "Yes," says Toto. Later, the man ruffles Toto's hair: "You're a man now." Later still, Toto, alone in front of his bathroom mirror, inspects the purple welt on his chest, fascinated.

Roberto (Carmine Paternoster) is lucky enough to land a job with Franco (Toni Servillo), a respectable middle manager for a toxic-waste-disposal company. Franco is happy to be a mentor to the young man. But Roberto, perhaps the closest character to a cleanskin in the film, gradually becomes horrified by the realities of southern Italy's waste-disposal practices. Through his eyes we come closest to questioning what, exactly, is morality in this amorphous world. When a drum of acid spills in an illegal quarry and a truck driver is burned, the drivers all walk off the job. A quick-thinking Franco rounds up some local children, and we are treated to the bizarre sight of nine-year-old boys, propped up on pillows, at the wheels of the massive vehicles. Everybody pitches in. The Camorra is in the bones.

The fifth storyline involves Pasquale (Salvatore Cantalupo), a tailor who works in the black-market economy for a Camorra-connected firm subcontracted by an haute-couture company. (The Mafia are deeply involved in the fashion industry, too, both in high fashion and the knock-off trade.) When Xian (Zhang Ronghua) offers Pasquale €2000 in cash per lesson if he'll give ten dressmaking classes to the Chinese employees in his sweatshop, Pasquale finds the offer too tempting to refuse. Each story strand has its surreal moment; here, it's when Pasquale walks into the sweatshop to give his first lesson and receives a standing ovation from a hundred polite Chinese workers. His story shows the compromised life in action: how you can be somehow connected to the world of crime, and trying to maintain integrity by making your living at something you both like and are good at. At film's end, Pasquale's tale will offer, too, the closest thing to a vision of an alternative fate.

That all these stories were taken from real life (via the best-selling book by Roberto Saviano) makes watching them all the more gripping and unsettling. Everyone in the film is part of this dense web of interconnectedness. At one point Pasquale notices, on a TV in a bar, Scarlett Johansson in a typical red-carpet moment, with commentators analysing her beautiful dress. By now we have an idea of the path a gown like that might travel before reaching Johansson.

The film chillingly intersects with real life in other ways, too. Some of the actors were professionals; others were colourful local characters who fitted into the story. Recently, Bernardino Terracciano, who plays Uncle Bernardino, one of the bosses in the film, was arrested for Mafia-related activities. Roberto Saviano believes Naples has all but surrendered to the criminals. He has been living under police protection since the possibly suicidal moment last September when he named the local Camorra bosses in a public speech. "Iovine, Schiavone, Zagaria," he said, "are worth nothing. Their power is founded on your fear. They must clear out of this land." Umberto Eco, rallying to Saviano's defence, went on TV to say, "in this case, appeals to writers for solidarity are of no use ... We know where the threats are coming from; we know the Christian and surnames of those who are making them. What's required is a public intervention by the state." In a land where judges are regularly blown up in their cars, it's an intervention that may be some time coming.

The term ‘organised crime' is one of those semantic units in our linguistic DNA that pops up in association with ‘the Mafia' or ‘the mob'. But it's a strange notion: crime that has been arranged and assembled, codified and marshalled into a way of life. For the residents of a region like Campania, that way of life becomes their way of life. There's no inside and outside, no real choice. In Matteo Garrone's blighted purgatorio the secret society has become society itself.