Rilo Kiley, Koko, London

Formed in Los Angeles around the former child actors Jenny Lewis and Blake Sennett in 1998, Rilo Kiley are hard to pigeonhole. Their first two, independent albums found themselves filed somewhere between alt.country and nu-folk. But labels and categories cannot do justice to a wildly eclectic style that marries elements of folk and country, indie-rock guitars, breezy Sixties-influenced West Coast pop harmonies and a spirit of adventure.

In Lewis, they have a glamorous performer with rare charisma, a literate lyrical style and a distinctive voice that can veer from a fragile folkie whisper to full-throated country wail.

She saunters on stage in a preposterously short Sixties mini-dress and knee boots, dwarfed by her giant guitar. Combining coquettish guile and childlike innocence, she has the audience in the palm of her hand.

On the optimistically/ ironically titled "It's a Hit", she simultaneously sounds as sweet as an angel while spitting venom in a lyric that attacks the political posturing of her government. It's a typical contradiction from a singer and songwriter whose speciality seems to be transforming heartbreak and pain into uplifting catharsis.

As she switches between guitar and piano, her keening voice lights up miniature dramas of lost loves and lives, charting the emotional terrain of modern relationships. Disappointment, deceit and death are recurring themes; where we might look for redemption, we find only fatalism.

Sennett jostles for attention with Lewis, his versatile guitar-playing skipping through the styles, from acoustic folk fingerpicking through bluegrass-style strumming to full-on psychedelic rock; in the encore he plays a ukulele.

The band explore their country side on "So Long", with its gentle harmonies between Sennett and Lewis, and the gorgeous title track of More Adventurous, while Sennett takes his turn in the spotlight for the old-time stylings of "Rip Chord".

There's more communal singing in the New Wave-y single "Portions for Foxes", with Lewis's ominous but strangely euphoric chorus: "It's bad news, baby, I'm bad news." But the highlight is the astounding "I Never" - not so much a pastiche of deep country-soul as its apotheosis. "I've lied, cheated, stolen and been ungrateful for what I have," sings the lovelorn Lewis, while looking as if butter wouldn't melt in her mouth.

In the past year Rilo Kiley have started to make waves, with wild acclaim for their third album, More Adventurous, and an upcoming support slot on Coldplay's American tour. It's a challenge they will relish.

Rilo Kiley play T in the Park, Kinross, tomorrow