The Frontline, Globe Theatre, London

Ché Walker must be the only contemporary dramatist who has written a play while dressed in doublet and hose. To get a feel for Shakespeare's Globe, he secured a small role in last season's production of Othello. He apparently penned The Frontline in the attic during the two-and-half hour gap between his appearances in acts one and five. It's a nicely ironic situation – a playwright in costume producing the first new play at the reconstructed Globe to be set in the here and now.

In The Frontline, the stage swarms with the messy multicultural life of our post-Imperial metropolis. The scene is the environs of a Tube station in a seedy North London street, dominated by the neon-lit entrance of a sexual "fantasy bar". It's amusing see the Globe's distinctive Pillars of Hercules swathed in pervy black plastic for the occasion. And, for the rain-soaked premiere of Matthew Dunster's engaging production, the groundlings too were sheathed – in the condom-like plastic macs which are handed out at this address. "Jesus gave me water" sing the brigade of born-again Christians at the start, arms raised heavenward. Verily, the Lord provides, and there are times when he provides too much.

A cast of 23 play a motley crew that include drug-traffickers, lap-dancers, a comically bookish club bouncer, warring gangs of young Somalis and Ethiopians, and a sad old man who imagines that every woman he encounters is his long-lost daughter, regardless of age or race. Walker knows how to work the crowd and he has a natural instinct for finding the poetic rhythms in stylised street talk. But there are confusing passages where he employs the Altman-esque technique of overlapping dialogue. Two groups of people compete for our attention simultaneously, and, in the resulting Babel, neither wins. Some key facts and significant remarks get lost or are only half-heard.

The problem of focus extends to the structure. Ben Jonson provided a rich, pungent panorama of London life in Bartholomew Fair, one of the Jacobean plays that furnishes a precedent for a drama like The Frontline. But there's comic velocity in his plotting and the diverse strands of his play keep intersecting in revelatory ways.

By comparison, The Frontline feels frustratingly bitty. Characters can drop from sight for lengthy periods so that you can barely identify them when they re-emerge for their next turn

There's no main protagonist as such, but the most important figure is Beru Tessema's Miruts, a strutting, handsome, weed-selling Ethiopian who, fatally, steals a bag of cocaine from a dealer, the thuggish white supremacist Cockburn (Robert Gwylim). Miruts's refugee father was a professor back home and is now a taxi driver puked on and abused by racists. Donna, the shrewd Underground worker who eventually beds the boy, poses the crucial question: why is this intelligent young man wasting his potential in an activity that prolongs the problem – pushing harmful products that fill people with paranoia and rob them of their ambition? In a vicious double bind, drugs both sustain and destroy. How free is Miruts to conduct his life differently?

The cast bring great zest and personality to a play that swings between preachy old-fashioned agit-prop and warm, well-observed humour, and between hip street-cred and a haunting sense of present-day London sitting on top of many rich layers that complicate the picture of our cultural heritage. The first half ends with a rap chorus tendentiously proclaiming that "The war on drugs is juss a war on blacks/ Is juss a big fat lie/ Like the war in Iraq".

And while the production generates an attractively communal atmosphere, there are times when you seem to be taking part in a liberal group-hug. No one heckles when the new Mayor of London is vilified as a racist, nor shouts, "what about Magna Carta, mate?" when the Afghan trader, Mahmoud (Kevork Malikyan) twinklingly proclaims that the only great achievement of the savage English is Marmite.

To 17 August (020-7401 9919)