Virginia Rodrigues, Queen Elizabeth Hall, London

Nobody knows where Virginia Rodrigues got her extraordinary voice - not even the singer herself. It wasn't the prevailing mode in the Bahian shanty town where she grew up, nor is it standard style in the candomble religious gatherings where she is now an initiate. Those who hear it for the first time tend to react like trees struck by lightning: from the theatre director who chanced to hear her in church, to the record producer who heard her on stage, everyone instrumental in her career has obeyed its dictates as though powerless to do anything else.

Since the Queen Elizabeth Hall was packed - and not just by London's Brazilian community - it's clear the word is out: two small-label CDs are circulating, her new Deutsche Grammophon CD Mares Profundos has just hit the shops, while The New York Times's label "the new voice of Brazilian music" has stuck like a burr. I'd heard her sing in the theatre, and listened to her recordings, but despite my admiration I did wonder how she'd sustain a whole evening. Because the whole point of her singing is pared-down simplicity: her timbre lies somewhere between a clarion and a countertenor, and her melodies are straight-up-and-down diatonic, without a trace of blues-style note-bending or melismatic embroidery. Would not 90 unadulterated minutes of that be a mite, well, boring?

She sailed on stage in billowing yellow silks: a tiny spherical figure on eight-inch heels: a massive presence commanding attention. Her quartet struck up round her, and instantly she was off, as though continuing a conversation she'd just left off. An Afro-samba by that inspired Brazilian duo Baden Powell and Vinicius de Moraes: an invocation of the candomble sea-goddess Yemanja. And as she sang, she herself seemed to be floating on the ocean, her tiny hands waving like those of a mermaid, her face in dreamy repose. The song was a miniature drama, whose human protagonist was drawn down to the deep where she merged with the divine. Rodrigues had us hanging on every note.

All the songs came from her new Afro-samba cycle, and though she never varied her luxuriously lazy pace they had a variegated brightness. No matter how inventively her musicians descanted round her, her singing remained imperturbably the same. Whenever she gave them their head they responded with bursts of casual brilliance; shimmying seductively with her percussionist, shaking as though at a candomble ceremony, she was constantly in motion despite the gravitational pull of what she laughed off as her "120 kilos of lightness". She made her exit like a ship sailing off into the night, then returned to sing a ravishing a capella song about the joy of singing. She hadn't traded, as another singer might, on the pathos of her origins, but she'd drawn us irresistibly into her world.