'I needed the plangent, plaintive music of the 12th century to understand Hugo's pain' – Katherine Langrish on The Undercover Soundtrack

We're getting medieval this week on The Undercover Soundtrack. My guest is Katherine Langrish, the acclaimed author of several fantasy novels for children and young adults, including the Troll Fell trilogy. She says she usually has to write in silence – but her latest novel, Dark Angels (The Shadow Hunt in the US), didn't come alive until she found her way to the 12th-century troubadour songs of southern France. Pull up a chair to the red blog and let her spin you a magic, medieval tale.