Nick Cassavetes is the son of one of America's most revered film directors. John Cassavetes (1929-89) made cheap cinema look intellectually respectable. He was pure jazz. His shooting style was fast and loose, and his plots were ugly. But he adored actors. He encouraged them to improvise. Some say he is the godfather of modern cinema.

The young Cassavetes has always been in awe of this magic. He inherited the desire. He inherited the stars. He's made expensive films. But precious little has genuinely clicked. Even by art-house standards, Nick's career has had to unfold under the most intimidating of shadows. He has been blessed with advantages his father could only dream about. He has secured parts as an actor in a healthy spread of Hollywood fare. He has directed glittering casts in films that perhaps promised more than they delivered. But Alpha Dog is topical and controversial; the story clearly shines with his own useful disillusions and search for artistic point. I suspect Cassavetes Sr might have been pleased.

It is the first film Cassavetes has shot in anger, and it rings worryingly true. The tabloid details are all too familiar. The director lays out the acts like a court case. There are subtitles announcing who is whom and an endless list of times and dates. This is because the film is the "fictional" mirror of a real crime that narrates the six-year pursuit by the authorities of an LA drugs king-pin.
A gang of white, rich kids is running rampant in the middle-class districts of LA. They are Eminem clones with respectable parents who are too busy to care. Emile Hirsch will never play a role as fabulously cruel for the rest of his career. He is Johnny Truelove, a drug dealer and would-be Tony Soprano. He has cash, girls and sacks of drugs. Most of all he has Bruce Willis (armed with a convincing hairpiece) as his father. We know Bruce is mean meat from the first scene. He is sitting in an armchair in his bungalow being interviewed about a murder that may or may not involve his wayward son. A tiff between the local Nazi nutter, Jake (Ben Foster) — who can't pay his crack bills — and the arrogant Johnny sparks an insane plot.

If the film wasn't based so closely on the truth it would be hard to swallow. It took two years for Cassavetes to picklock the legalities.

Johnny persuades trusted members of his gang to kidnap Jake's 15-year-old brother, Zach (a great and humbling performance by Anton Yelchin). The wisdom of this clumsy snatch is quite lost on Justin Timberlake. He is Frankie, and he has the attention span of a slug. He is Johnny's best friend, and the unwitting heart of the movie.

Johnny charges Frankie to guard the kidnapped boy. Frankie promptly forgets his jail duties. He likes Zach, and Zach doesn't mind being kidnapped. Frankie's dad has a huge swimming pool. The deck chairs are full of teenage totty, and the cast is contractually obliged to ignite a large Camberwell Carrot every ten minutes. Zach, the prisoner, has never had it so good.
Cassavetes assembles his chilly twists around Hirsch. The actor's eyes glitter with deadpan pleasure. His character Johnny is demonic. He might be Pinky from Brighton Rock, or a young James Cagney. But that's too exotic. Hirsch wears a back-to-front baseball cap, a mobile phone and a smirk. The cruelty is banal. That's the creepy power. It helps that his father is the neighbourhood bruiser. And it's a given that his No 1 desert island tune would be Guns and Bitches by Gangstas in the Hood.

This sheer lack of communication is the honest and electric shock. No one, including Willis, is immune. The real crime is that the entire morality of a generation is being tapped out by teenagers on mobile phones.

Cynics will doubtless fear Alpha Dog for all the wrong reasons. They will fume about its credibility. They will wonder about the phenomenal number of tattoos on show. They will link the casual horror of this film to Monday's murders in Virginia.

True, Alpha Dog is a film with no manners. But it has great nerve. What's truly impressive is how the splintered story is buried by individual performances. That shows great skill and brave directing. Timberlake is a revelation as the Pontius Pilate of thugs. His fealty is tragic. It twists his wits. It contradicts conventional wisdom. But that's the nature, and loyal demand, of friends. I think many teenagers will enjoy and understand this.