Screams in the darkness. A girl running onstage, bloodied, desperate, terrified. Alone on stage, she is caught, struggles but is brutally raped and then strangled with her own underwear.

This opening image, all the more powerful for being played out by the actress (Kedibone Tholo) all on her own, is as devastating a beginning as you can imagine. There are other startling moments in this angry, sprawling large-scale piece from the dark heart of the “new” South Africa.

Township Stories has an impeccable pedigree, co-written by Presley Chweneyagae (who played the title role in this year’s Oscar-winning foreign language film Tsotsi) and Mpumelelo Paul Grootboom, who, at 22 and 31 respectively, are two of the hottest young talents around.

Grootboom has been saddled with the nickname of “the Township Tarantino” because his scripts are full of unremitting violence, in this case including a grim succession of rape, self-induced abortion, beating and death. There is no glorious choral singing here, no gumboot dances; the one possible romance is snuffed out by the surrounding savagery.

As a social document, that makes this an important piece, although it is uncomfortably noticeable that Aids, the one affliction that hangs over all South Africa like a pall, is never mentioned. As a piece of theatre, though, it is wildly uneven.

There are moments of great power, as already indicated. The opening of the second half is another; a man viciously beats his pregnant teenage girlfriend while the rest of the 16-strong cast process around them, casting articles of clothing to the ground with every blow, all accompanied by the voice of Carole King singing Will You Still Love Me Tomorrow?

This is a good trick, but Grootboom, who also directs, plays it so often, with all sorts of popular music from Paul Simon to Marvin Gaye, that it becomes an instant cliché. He also makes the mistake of repeating the opening rape scene, this time with the girl’s assailant actually present, at the end.

But the biggest problem is the writing, which rarely rises above the level of second-rate melodrama and leads to moments, not to say extended periods, of risible bathos, even among the bloodshed. Did no one at the Traverse actually read the script before agreeing to programme it at the home of new writing in Scotland? Or were they seduced by the show’s sensational reputation? Don’t be.

Box office: 0131-228 1404, until Sept 2; then touring to Exeter, Nottingham, Poole, Winchester, Birmingham, Manchester, Ipswich and London