At Millbrook Prison, in 1874 London, the reader meets Margaret Prior, a lady "Visitor" who comes to offer solace to the female inmates. Our Miss Prior has recently been ill, recuperating slowly from the death of her beloved father, now determined to commit her energies to the less fortunate. Millbrook Prison is a huge edifice of gothic proportions, towers and tunnels and geometric patterns leading to the stark chill of individual cells, where the greater part of each prisoner's day is spent in isolation.

Miss Prior is interested in the lives of the women prisoners -- particularly Selina Dawes, a spirit medium jailed for fraud and assault, who seems a gentle, if lonely, soul. Miss Prior is Selina's solitary visitor, beside the "spirits" that whisper encouragement every evening when the lights are extinguished.

This is Victorian England at its apex, when women of Miss Prior's class are wrapped in innocence, nursing a constant need for comfort and protection. When Margaret forms an attachment to Selina, she keeps her thoughts to herself, speaking only through the pages of her diary. The obsession appears to be mutual; Selina calls Margaret "Aurora", promises that Margaret is her "affinity", that together they are two halves of one whole.

On a bitter January day, Margaret visits Selina one last time, the night chosen for Selina's carefully plotted escape. Margaret has made secret preparations: passports, travel arrangements, clothing, adequate funds. Selina promises to come for her beloved "Aurora" before dawn. Does Selina escape, and what are the consequences of this act for Margaret? Affinity is a masterpiece of the tension of the unexpected. Page by page, author Sarah Waters beguiles the reader, step by step through a twisting maze, as she leads us to the shocking denouement of her masterful tale.