Inverness, 1769. On a freezing winter's night, astronomer Nancy Lockaby arrives at Blackthistle House, home to renowned Shakespeare scholar Caleb Malles, to assist him in his research. She hopes to forget all that has happened to her in London.
Nancy initially finds herself captivated by Caleb's eccentric mind and deep passion for Macbeth.
So, when she is warned by three mysterious women that Caleb is keeping secrets from her, she is dismissive - after all, the women also claim to have lived many centuries and possess powers that defy any logical reasoning. Yet, as Caleb's behaviour becomes more erratic, she begins to suspect that she has walked into a trap.