John Fordham sees Nina Simone bring the Barbican to its feet (and that was before she'd started to sing)

From the moment the great soul-jazz diva came on stage, it was as if the countdown had been started on a firework extravaganza, but one designed by an artist with a loose wire or two. For with Nina Simone you never know just how much of the show is going to go off, or when - or even whether it will go off at all. There's an air of fearful expectation accompanying Simone's performances which compounds the already formidable effect of her whiplash tones, her alternately drumlike and elegiac piano-playing, her baleful stares and her bruised and brooding stage presence. When she was regularly appearing at Ronnie Scott's during the 1980s, her shows were among some of the most unforgettable public performances of recent times. 

Here at the Barbican, Simone was winding up the London WOMAD festival's Global Spirit weekend, following a powerful bill that featured various interminglings of Somali, Arabic and Western music. She thus found herself in a surreal environment where most corners of the venue's stark concourse were occupied by stalls selling pots, paintings and coats of many colours. 

The surrealism was enhanced by an introduction that meticulously listed her considerable honorary titles and brought the house to its feet before she had even been guided to the piano stool. An aside to her band, a few hesitant steps towards the footlights, the merest shadow of a smile, and the roof almost fell in. 

Simone has often behaved as if her muse and her music are hard-won prizes not to be given away lightly, even to paying customers. And at the start of the set it seemed as if she would deliver a series of brief sketches of the dimensions of her talent, then go home. This effect was compounded by the attentiveness of her band, which is rather fussy for the stark, penetrating clarity of her work, and by the inescapable fragility of some of her pitching, which the group's approach may have been designed to camouflage. 

She began with what she described as Bloodsongs, a series of gospel and African-flavoured pieces that she traced back to her own childhood, but though these songs trembled with the occasional shard of raw Simone energy, they were mostly muted, and Here Comes The Sun was the most muted of all. 

If this was Simone's concession to the event she was participating in, the audience was waiting for something else. But when she sang I Loves You Porgy, it was as if the first flashes from the firework display had begun to pierce the murkiness. 

Simone immediately responded to an audience request for The Other Woman, and a sinister eagerness began to tinge the music.

She spat out My Way with a new ferocity, and Pirate Jenny, one of her most spine-tingling interpretations, was delivered with an edge that rolled back the years. The audience went ballistic, the more so for the artist's stately progression to the front of the stage, head slowly panning around the auditorium, smile slowly spreading in what was clearly something near elation. 

'Since you're all standing,' she said, 'I'd like you to join me in singing We Shall Overcome.' We did. And when she went off into a huddle with the knot of anxious minders who hovered in the wings all show, the noise intensified. So back she came, to deliver, of course, My Baby Just Cares For Me. A performance that had begun in the hazy middle distance had come up and hit its witnesses right between the eyes. The baffled genius, it seemed, had suddenly remembered the point of it all.