Lady Sovereign, Scala, London <!-- none onestar twostar threestar fourstar fivestar -->

"You's in the midget's mansion now," spits Lady Sovereign, the diminutive MC from the Chalkhill Estate. But "Sov" - born Louise Harman in Wembley in 1985 - has travelled a long way from her north-London roots. Three years ago, she was the darling of the grime scene, making people laugh and move in equal measure to witty tracks like "Ch Ching". But Grime never quite broke out of its underground base, and the foul-mouthed little strumpet was forced to look to America for recognition. In 2005, she got just that when, after a personal audition with Jay-Z, she signed to his Def Jam label, joining such hip-hop luminaries as The Roots and Nas.

So, when she appears at the Scala in King's Cross in front of a baying collection of tracksuits and jauntily angled caps, she does so as a local girl done good. Her debut album, Public Warning, has been a hit in America. But - with the occasional cringeworthy cross-cultural reference (does Sovereign really live in a "council apartment"?) - it marks a slight departure from the unabashed street patois with which she attracted her fans.

Not that they care. Tonight, Sovereign appears - with her hair in the trademark half braid, half pigtail - in baggy jeans, gold-on-black T-Shirt, hoodie, and wraparound shades. And, to the accompaniment of decks, bass guitar, drums and her diehard fans mouthing their favourite lines, she mixes up old and new tracks. It's a spirited set - Sovereign bounces around the Scala's stage like a toddler - but is hampered by a sound system that lets down both artist and audience. "I can't hear myself up here," she complains. The crowd receive a fuzzy vocal too.

It's a shame, because her wit shines through on individual lines, such as the derisory "Broom": "Stupid little bitch, don't be starting riots/ If you wanna be starting something, why not start a diet?"

By the end of the evening, though, one has the impression that it is Sovereign who is punching above her weight. Although her delivery is strong, her material does not quite hold the room's attention. Perhaps that's because she is finding it a little hard to keep her own attention. "I'm pissed," she admits, looking every inch the Friday night troublemaker.

There is one great communal moment in the set, when "the biggest midget in the game" leads the crowd in a rousing rendition of "Happy Birthday" for her DJ. But, personal celebrations aside, Sov has yet to crack the secret of holding a room in her tiny hand.