Olwen Mellory is called away from her life as a writer of fairy tales to take part in a week-long retreat on a remote Scottish island. 'The Great Journey' promises to be full of magical wisdom and visionary experiences. It's an invitation she can't resist.

But within hours of arriving at the imposing Dunesfort House and meeting her companions in the circle, Olwen's adventure takes an unexpected turn. Before long, her daytime explorations of mystical practices are paired with night-time dreams and phantasms that blur the line between the real and the imaginary. As the enigmatic but vaguely sinister course director asserts his authority in a bid to create an act of modern alchemy, Olwen begins to wonder in whom she can trust.

After a shocking event in the circle Olwen flees across the moors to the Callanish Stones, only to find herself caught in an ancient moon rite. Will this final calling free her from her personal demons forever, or will it be the beginning of a new nightmare?