Rachel Unthank & The Winterset, Spitz, London

The Spitz's month-long festival of folk entered its final week – along with the existence of the venue itself – with the return of the Northumbrian all-girl quartet whose album The Bairns has been hailed as one of the folk albums of the year.

The group came together in 2004, with singer and cellist Rachel Unthank joined by her sister Becky, viola player Jackie Oates and the versatile pianist Belinda O'Hooley. Oates left earlier this year, to be replaced by the fiddle player and singer Niopha Keegan.

The Unthanks were raised in English traditional music, especially that of the North-east – their dad George was a member of The Keelers, a rowdy male harmony group. O'Hooley comes to the folk repertoire from a very different circuit; a singer-songwriter whose day job was playing everything from music hall and wartime songs to big band and Twenties jazz numbers in homes for the elderly.

This mix of very different traditions gives The Winterset their unique sound. O'Hooley's virtuoso playing can skirt the outer reaches of cabaret and parlour piano. Augmented on some songs by a string quartet and double bass, The Winterset provide an evening of stunning vocal harmonies and spare instrumentation.

They open with "On a Monday Morning", with Rachel Unthank's voice and O'Hooley's piano building from stark minimalism to full four-part vocal harmonies. Becky Unthank takes the lead on Sheila Stewart's "Blue Bleezing Blind Drunk" before leading the audience into a choral singalong on "When the Tide Comes In".

O'Hooley's originals include the lilting "Blackbird", written specifically for Becky's enveloping, velvety voice, and the intense "Whitethorn", about a bush in her father's village in Sligo that marked the 13 graves of her great-grandmother's still-born children.

Each member can carry a lead vocal, but it's when all four are engaged in the exquisite rise and fall of their four-part harmonising that the hairs rise on your neck. Intimate, epic, overflowing with feeling and musical intelligence, The Winterset have everything to play for.

Touring to 3 December (www.rachelunthank.com)