As usual Sarah Waters researches her period extensively, even capturing the styles and patterns of speech used in 1870s England. You become seduced by the first person narrations of Margaret (the lady visitor to Millbank prison) and Selina (the prisoner and spiritualist). However, Margaret's story fills the bulk of the novel and it's extremely easy for the reader to adopt her perspective, despite a twenty-first century scepticism about spiritualism. Seances went through an extremely popular phase in Victorian England, so Waters is writing about something that was accepted and believed at many levels, hence Margaret's fascination with Selina and her total belief in her.
I wasn't spellbound or captivated by the paranormal aspects of the novel and fathomed out the ending before it happened, but nevertheless found it a fascinating and well plotted tale that explores some of the darker undercurrents of nineteenth century London, the lives of ladies and convicted prisoners and the Victorian penal system.