Inverness, 1782. On a freezing winter's night, astronomer Nancy Lockaby arrives at Blackthistle House, home to renowned, enigmatic Shakespeare scholar Caleb Malles. When, a month before, Nancy received an invitation from Caleb to leave her position at the Royal Observatory and join him as a research fellow, she saw the opportunity to leave behind a past riddled with tragedy - and to find adventure and freedom in Scotland. In her new home, Nancy finds herself captivated by Caleb's eccentric mind and deep passion for Macbeth. So, when she crosses paths with three old crones who reveal 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 the mysterious scholar might have had hidden motives.