Margaret Prior is an well-to-do spinster who is recovering from her father’s death and her own failed suicide attempt. Hoping to bring some purpose to her life, she volunteers as a ‘Lady Visitor’ at Millbank Prison. There she becomes entranced by Selina Dawes, a spiritual medium imprisoned for fraud and assault.
The story covers a two year period and is revealed slowly with chapters alternating between the present and the past events that led to the present situation. The sense of suspense builds as the story progresses to the point where even the rational reader cannot tell what is supernatural and what is not. The story is so skillfully told, leading the reader to identify fully with Margaret and her dreams and hopes, that the outcome is a shock yet so plainly obvious.
Waters vividly recreates the gloom and depersonalizing rigidity of the prison system in the 1870s as well as the equally imprisoning social strictures of wealthy English society.

A detailed review can be found here.