In an age of 90 minute, three character studio plays, Who Killed Mr Drum? - an epic new 12 character play that runs for some three hours and ten minutes - is certainly a departure. But sometimes it can be a case of too much of a good thing; and this big, sprawling, ambitious play occupies a dense canvas of plot and character that sometimes goes in several directions and pursues a lot of different complicated strands at once.

Writers Fraser Grace and Sylvester Stein make use of the leisurely, talkative traffic in and around the offices of South Africa's first black magazine, Drum, in 1957, to convey messages about black life that make it feel rather like an August Wilson play.

But while the period it charts, with the tightening grip of apartheid on South Africa, has an undeniable fascination and historical importance, I do wonder, too, why a black British play has once again had to go beyond our own borders for its subject. Black British stories are too rarely told - and if the nearly simultaneous arrival of The Big Life and Elmina's Kitchen in the West End earlier this year marked something of a revolution in putting them on central London stages, here we get another in a long line of South African stories.

Though set amidst journalists this is no Front Page. The stakes are far higher here, with former Drum editor Stein creating a play with Grace based on his own, true-life 1999 investigative memoir of the death of a colleague on the magazine - the eponymous but officially anonymous Mr Drum, who went "undercover" to expose the country's various and multiple hypocrisies and helped to make the magazine's name.

Looping backwards and forwards from the discovery of his murdered body on a street in Sophiatown, Johannesburg, the play brings both his work and that of the magazine into variously sharp focus, and the policies of 'separate development', as apartheid was euphemistically dubbed, that prevailed at the time.

Designer Francisco Rodriguez-Weil provides an evocative set, with the magazine office, a shabeen and a bedroom folding into and out of that Sophiatown street.

In the same way, the play, too, folds several competing stories within it - part illegal love-story across the racial divide as the magazine's deputy editor Can Themba has an affair with a married Englishwoman; and part murder mystery, as the journalists try to solve the riddle of their colleague's death.

Paul Robinson's production is keenly inhabited by a crack ensemble cast, with particularly effective performances from Stephen Billington as editor Stein, Sello Maake Ka-Ncube (the RSC's most recent Othello) as his deputy Can Themba, and Wale Ojo as the murdered Henry Nxumalo.

But while the play is compelling at times - and builds to a particularly vivid climax and a moving postscript about where the real-life characters ended up - it needs to be tightened up structurally.

- Mark Shenton