Marian Taylor, who has come as a "companion" to a lovely woman in a remote castle, becomes aware that her employer is a prisoner, not only of her obsessions, but of an unforgiving husband.

Hannah, the Unicorn, seemingly an image of persecuted virtue, fascinates those who surround her, some of whom plan to rescue her from her dream of redemptive suffering. But is she an innocent victim, a guilty woman, a mad woman, or a witch? Is her spiritual life really some evil enchantment? If she is forcibly liberated will she die? The ordinary, sensible people survive, and are never sure whether they have understood.