A tale of the North Berwick witch trials. It's the 4th of December 1591. On this, the last night of her life, in a prison cell several floors below Edinburgh's High Street, convicted witch Geillis Duncan receives a mysterious visitor - Iris, who says she comes from a future where women are still persecuted for who they are and what they believe. As the hours pass and dawn approaches, Geillis recounts the circumstances of her arrest, torture, confession and trial, while Iris offers support, solace - and the prospect of escape. Hex explores what happens when a society is consumed by fear and superstition, and how a king's crusade against ordinary women can still be felt up to the present day.