This delicious period piece, based on Sarah Waters’ 1999 novel of the same name, is a women-in-prison movie with a gothic Victorian twist. Upper-class Margaret (Anna Madeley), mourning her father’s recent death and looking for diversion, goes to Millbank Prison as a “Lady Visitor” — presumably to improve the female convicts but really as a way to step outside her limited, conventional world. When she finds herself irresistibly drawn to Selina (Zoe Tapper), an attractive young convict, Margaret’s do-gooding quickly falls by the wayside.

Nothing is what it seems as Margaret becomes smitten with Selina, who once enjoyed celebrity as a successful medium before being convicted of fraud and the mysterious assault of a young girl. Fans of Sarah Waters (Tipping the Velvet, Fingersmith) will be happy to know that screenwriter Andrew Davies, fresh from adapting Jane Austen for the BBC, hews closely to her dark and eerie second novel. In preserving the atmospheric mood of the disturbing thriller, Davies faithfully transfers to the big screen Waters’ fascination with the seamy underbelly of Victorian propriety, where ladies’ frustrations find outlet in private sessions with a medium, and benevolence is a fragile facade for voyeuristic fascination.

Stylishly shot, Affinity features stellar performances from Anna Massey, Amanda Plummer and particularly Madely, who does a superb job of conveying the unspoken longings of the intelligent and frustrated young Margaret, who is as much imprisoned by her gender and class as the mysterious Selina is by bars and chains.