The story was about Margaret Prior, a 30-year old spinster with a troubled past who acted as a visitor to the Millbank Prison and met the beautiful prisoner, Selina Dawes, there. Selina was a spirit-medium who accidentally caused the death of a patron during one of her sittings.
The 19th-century women goal's setting and an exploration of spiritualism lent the novel mystery and suspense. But it is far less enjoyable than the author's other works. The lesbian relationship (Waters' common theme in her novels) was something expected, and it had taken too long for it to develop. Also, presented in the format of the journals of the two ladies, the novel reads like a record of their encounters and it is not very exciting.
However, Waters never ceases to surprise her readers. There is a very shocking ending which makes all the plodding though the laborious account worth the while.