We should think twice before we sigh at the idea of a street crime musical. After all, Giant Olive has made this Kentish Town pub a diary regular in recent years; their best work has been thrilling and even their patchier efforts achieve a vibrancy we see too rarely on the London fringe. So remember West Side Story and prepare for sixty breakneck minutes of street talk, beatbox rap and menace.

Penned by director Ray Shell, along with other hands, Zip is a turf war tale with a twist. Four young people people pair off for a drug-fuelled night in a derelict warehouse. Or maybe not so derelict, as the place is also home not only to the dangerous Kalipha Krew, who are using it as a weapons stash, but to the souls of the dead young people who have been murdered ("merked") on local streets. Some of the living may join their number before the night's out.

The premise is simple: the living world is played straight while the dead world is sung and danced. Fifteen performers squeeze into the tiny upstairs space and in Gary Lloyd's fizzing choreography make it feel twice the size. Talent is spread unevenly among the ensemble, but the best of the chorus shine like good deeds. Victor Henry Muir achieves a painful intensity in his brief solo moments, while Todd Holdsworth is a dancer to be reckoned with: properly low-key in repose but riveting when the hoofing kicks in. The "living" characters are played by more experienced actors, not all of whom can make much sense of the shouty, squabbly script. Really, would teenagers like these be able to mouth off quite so much? It's hard to be frightened of a gun-toting Krew that's always up for a debate, however loud. Semi-articulate rage would be far more disturbing because of the pent-up frustration it would signify.

Beau Baptist as the wannabe terrorist Reffessi gives the night's truest performance, and there are persuasive contributions from Mark Gillham, Jack Guttmann and co-author James Kenward. The female characters are well enough played by Alma Eno and Jennifer Oliver, even though Ray Shell gives them little of interest to do.

The show's hour is packed with twice its own weight of depth and material, and the pace and commitment are terrific. To succeed properly, though, it needs to clarify its message and communicate with a more balanced vocal arc. Audiences aren't moved by being yelled at. If that can be done, Zip has the potential to become a significant play.

- Mark Valencia