Margaret Prior (also called "Peggy" and "Aurora"), an unmarried woman from an upper-class family, visits the Millbank Prison in the 1870s Victorian era England. The protagonist is an overall unhappy person, recovering from her father's death and her subsequent failed suicide attempt, and struggling with her lack of power living at home with her over-involved mother despite being almost 30. She becomes a "Lady Visitor" of the prison, hoping to escape her troubles and be a guiding figure in the lives of the female prisoners. As she peers through a flap in the door, entranced by the sight of a young woman with a flower, she is reminded of a Carlo Crivelli painting. Of all her friendships with prisoners, she is most fascinated by this woman, who she learns to be Selina Dawes, medium of spirits.
The novel was adapted into a screenplay by Andrew Davies. A feature film based on Davies' adaptation of Affinity premiered on 19 June 2008 at the opening night of Frameline, the San Francisco International LGBT Film Festival, at the Castro Theater.
The film was first shown on ITV1 in the United Kingdom on 28 December 2008.
'It is a world that is made of love. Did you think there is only the kind of love your sister knows for her husband? Did you think there must be here, a man with whiskers, and over here, a lady in a gown? Haven't I said, there are no whiskers and gowns where spirits are? And what will your sister do if her husband should die, and she should take another? Who will she fly to then, when she has crossed the spheres? For she will fly to someone, we will all fly to someone, we will all return to that piece of shining matter from which our souls were torn with another, two halves of the same. It may be that the husband your sister has now has that other soul, that has the affinity with her soul—I hope it is. But it may be the next man she takes, or it may be neither. It may be someone she would never think to look to on the earth, someone kept from her by some false boundary...'