Cat Power, Barbican, London

I got them back-on-the-wagon blues

The first question on everyone's lips must surely be: is Chan Marshall going to have a meltdown tonight? The Atlanta-born singer-songwriter, who records under the name Cat Power, is infamous for all the wrong reasons. She forgets her lyrics, gives up on songs, sometimes even breaks down into tears. And for the second question: are we here because we want to witness a car crash, or an artist at the height of her powers?

There is a feeling of expectancy in the air. As she proudly declares several times during the show, Marshall is sober now, after years of on-the-road drunkenness. Not only that, she has one of the tightest backing bands on earth to prop her up - Al Green's Memphis Rhythm Band, including strings, horns and the saint-like Teenie Hodges on guitar - as well as a critically acclaimed recent album, The Greatest, which she performs almost song by song.

She takes to the stage barefoot, self-consciously waving away the applause, hiding behind her trademark fringe (which half of the girls in the audience are also sporting) and launches into the defeated, wistful album opener, "The Greatest". She's a beautiful woman, but she wears it like an old cardigan, with a shrug - dancing awkwardly on her tiptoes and jogging on the spot like a boxer. And then there's her voice: her recordings don't do justice to its girlishly smoky, seen-it-all timbre. With the Memphis Rhythm Band behind her, this tortured indie pin-up is transformed into a genuine blues singer - wringing the emotion out of her songs, as she wrings her hands.

Or, so I thought. During her solo interlude, the cracks start to show. At first, she grapples with a microphone stand. Then a cover of "The House of the Rising Sun" - which strips this most ubiquitous of songs to it bare, bloody bones - is sabotaged by her own anxiety. "I just wanted this to be the best show," she murmurs. "Shall I just get off the stage?"

Thankfully, this neurotic panto never goes full-blown, as it would have done a few years ago. For her encores (there were two), the stark "I Don't Blame You" from 2003's You Are Free, segues into a titbit from the Everly Brothers' "All I Have to Do is Dream", which, in turn, becomes "Blue Moon". Hank Williams's "Ramblin' Man" is given a ghostly, acapella treatment. But Chan never looks as happy as when she has her band around her - most notably, when they all huddle around the microphone for a cheerful rendition of Smokey Robinson and the Miracles' Motown classic, "Tracks of My Tears".

Chan Marshall is that rare thing - a female singer who doesn't exploit her own beauty, but expresses herself in the most integral way: through her voice. On a night like this, it triumphs over everything, even her fear.