A new stage musical often proves to be a long-term work-in-progress, and so it will be, I think, with Jack. The creation of composer Robin Martin-Oliver and writer David Staines, the show offers a gripping account of the grisly murders carried out by Jack the Ripper, and the fruitless efforts by the authorities to catch him. While an unsavoury subject matter is no barrier to stage success, a very obvious handicap arises here from the unsatisfactory ending to the story - the Ripper, of course, remaining obstinately uncaught and the subject of endless speculation about his identity.

Mr Staines holds back from 'fingering' a particular individual in his book. Less wisely, however, he presents no fewer than four characters as likely suspects: the occultist Dr Roslyn D'Onston (Gerard Smith), the Queen's physician Sir William Gull (Brian Conroy), cotton merchant James Maybrick (Nick Millward) and the American actor Richard Mansfield (Leejay Townsend). While clearly having tried to be historically accurate, Mr Staines lets himself down, it seems to me, by inventing a romance between Maybrick's wife (Stephanie Nielson) and the US thesp.

This further complicates a plot so convoluted that it requires two closely printed pages of summary in the programme. It is in the elimination of some of these complexities that I expect the writers to be engaged as they work to fashion a compelling entertainment from their very promising material.

The music is certainly one of the show's strong points. From the opening moments, with his evocation of church bells and other sounds of London, Mr Martin-Oliver sweeps us away to foggy streets of Victorian Whitechapel where a colourful gallery of prostitutes and their top-hatted clients roam. Operatic, somewhat Brittenesque, in tone, his writing for the singers is considered and almost always suitable. It seemed to strike a wrong note, however - to employ an inappropriate metaphor - when, after more than an hour of 'sung through' drama, the sound of unmusical speech was suddenly heard.

In his role as director, Mr Martin-Oliver might have spotted, too, that the excellent chorus number In Hell would have made a far better beginning (after the overture). The long 'aria' The Edge of Reason which he chose instead - from David Watkin-Holmes's Insp Frederick Abberline (pictured) - left its excellent singer dangerously exposed.