Fanny Kemble (Jane Seymour) is actually a woman ahead of her time. A published poet and an actress from a prominent English theatrical family, she has resisted marriage in favor of personal independence. But while touring America in the 1840s with a production of Othello, she falls in love with the wealthy Philadelphia lawyer Pierce Butler (Keith Carradine). "I want to do everything that can be done," she tells him; "unfortunately, I was born a woman." But he sympathizes with her spirit, and she recognizes in him a match for her wit, charm, talent, and smarts.

Immediately after they're wedded, however, he turns domineering and controlling -- all that he admired in her previously are precisely the qualities that are quite unsuitable in a wife. He forbids her to publish a journal of their life in Philadelphia, one critical of American society -- she does so anyway. But their biggest battle of wills erupts over the Georgia plantation -- and its 600 slaves -- that Pierce has inherited. Bored with Philadelphia and curious to see the South's peculiar institution firsthand, she convinces Pierce to move her and their daughters to Georgia.

What she finds on the plantation, Butler's Island, appalls her: deplorable living conditions for the slaves, women forced to have as many babies as possible in order to increase their owner's wealth, and men and women alike suffering inhumane punishments for minor infractions of the capricious rules. In a world where it's dangerous even to suggest that slaves are human beings, Fanny sets out to help those on Butler's Island, though this fires off her husband's raging temper. She oversees the building of a new slave infirmary, teaches the slaves to read under the guise of a Bible class, and, with the help of a like-minded local physician, Dr. Houston (James Keach), sends small groups of slaves off on the Underground Railroad to safety in the North. And all the while, she keeps a journal of her life on Butler's Island in the form of letters to a friend back in Philadelphia -- a necessary deception, as Pierce has forbidden her from journal writing.

Enslavement does not avoid the stories of the slaves themselves, though they do take a back seat to Fanny's. Some powerful performances, however, from actors in the slave roles make them unforgettable. Joe (Adewale Akinnuoye-Agbaje), a carpenter on the plantation, resists Fanny's help at first, rejecting what he sees as the cruel false hope she offers. His slow change of heart -- abetted by his wife, Psyche (Sharon Washington), who finds herself reluctantly touched by Fanny's friendship -- is extraordinary to watch. And young Jack (Eugene Byrd), assigned to Fanny as her "personal domestic," is the sweet-faced kid you know is too ebullient and loyal for his own good, but Byrd gives him the kind of life that elevates him beyond cliché.

Without ever cheapening the horror of slavery -- and several hard-to-watch scenes let us know how awful it was -- Enslavement manages to suggest that Fanny and Pierce were as much slaves to their time as the people kept as property were. Fanny, of course, is constrained by her gender and by her husband, limited in what she may say and do. And Pierce is never presented as evil, merely as a businessman carrying on with a family enterprise he may not have even wanted charge of. That's not meant as an excuse for his helping to perpetuate an atrocity that plenty of people at the time recognized as evil, but more an explanation. And, ironically, it's a token of how realistic a character Pierce is through most of the film that his sudden transformation at the end is a bit too pat to be believed.

But this detour into the melodramatic can be forgiven. Enslavement is Fanny's story, after all, and one that deserves to have been told at long last.