Set in and around the women's prison at Milbank in the 1870s Following the death of her father, Margaret Prior has decided to pursue some 'good work' with the lady criminals of one of London's most notorious gaols Surrounded by prisoners, murderers and common thieves, Margaret feels herself drawn to one of the prisons more unlikely inmates - the imprisoned spiritualist Selina Dawes Sympathetic to the plight of this innocent-seeming girl, Margaret sees herself dispensing guidance and perhaps friendship on her visits, little expecting to find herself dabbling in a twilight world of seances, shadows, unruly spirits and unseemly passions