"The Governess" is Mary Blackchurch's (her 'Christian' name) story. It is set in 1830s (we learn from the Daguerre reference) in London and the Scottish Isle of Skye, where she becomes a governess to help the family after her father is murdered. If we are to believe Ebert's instincts, it is the author's life story, much as "Boyz N the Hood" is.
Being a photographer, I was 'hooked' when the film turned in that direction. Although not historically accurate, it certainly does a good job of depicting the trial and error used back in the 1800s to master a photographic process in which the resultant image could be "fixed". There was a British Cavendish, Henry, but he was not into photography. In this film, Mary accidentally helps discover a fixing process using ordinary salt water. Mary and Carles develop a bond, become lovers, Mary talks of their "future" together, Charles pulls away, "You consume me. I cannot be consumed."
I cannot say too much about how fine a performance Minnie Driver gives here. Especially the scene near the end when she basically is willing to do anything, give anything, to avoid rejection by Charles. Failing, she returns to London, giving nude photos to Charles' wife, and taking along enough chemicals to get her started in her own photographic studio.
Charles looks her up, she does a portrait, but the love she professed had been shattered beyond repair. She had given her whole self to Charles, had been rejected, and she moved on.
This is a really fine film, different, but enjoyable in the vein of "Dangerous Beauty", another period piece where the female protagonist is empowered. The infidelity in "Governess" is certainly not glorified, but used in the context of a weak husband whose marriage was a routine formality, and a young girl who knew no boundaries, and found a soulmate for the first time.