As rain batters down on the roof of our tent, competing with the various noises particular to Edinburgh at this time of the year – fireworks from the Tattoo, the crashing drums and bass from the band playing in the Spiegeltent next door – our host for the evening quips “it’s like being in the womb of a mother at a Metallica concert”. But when Rachel Unthank stands to sing, she holds us all captive with her presence. It is just her voice, and the story that she is telling, that fills this space.

Sisters Rachel and Becky Unthank with pianist Adrian McNally are discussing and performing songs from their newest album, a compilation of tracks written by Molly Drake titled The Songs and Poems of Molly Drake. Mother to legendary singer-songwriter Nick Drake, Molly was also a songwriter in her own right, though she never released her music publicly. So when Nick Drake’s estate approached the Unthanks with the idea of bringing her music to a wider audience, they took a good listen and found a treasure trove of songs to work with.

Molly’s songs are full of emotional intelligence and empathy, the sisters tell us, which is what drew them to the project, along with the fact that they are folk songs in the storytelling tradition. While Becky and Rachel choose songs for their lyrical content, Adrian brings those stories to life with his complementary arrangements. It’s a partnership that works. When the sisters take to the stage together to sing What Can a Song Do To You there is a reverent hush. Their effortless harmonies are unhurried and filled with passion – it’s that emotional intelligence again, which transcends the lyrics, and which they both able to draw upon, bringing Molly’s internal world to life.

Much of this evening is spent in talk – questions from chair David Mitchell are answered and we have a few laughs about folk police and those pesky fireworks, but for me this is just marking time between songs. As interesting as the back story is, I can’t help but wish we were here to listen to the album in full, rather than hear the answer to questions about personal idols or what album each band member last bought. There is enough joy and sadness, pathos and light in the voices of the Unthanks to tell their own stories.