In 1837, Elisabeth Laurier, a French-speaking Swiss governess, agrees to bear a child for an anonymous English landowner in return for £500 needed to pay her father's debts. They meet over three nights at a coastal hotel and, despite their wish for detachment, develop a deeply passionate connection during their lovemaking by the firelight. Their feelings grow as they converse on the beach and during their time at the hotel.
Nine months later (10 August 1838), Elisabeth gives birth to a girl, and, as agreed, hands her daughter over to the care of the father. Over the coming years, Elisabeth never forgets her child, keeping a journal of watercoloured flowers and plants, adding a page for each holiday and each birthday the daughter celebrates while they are apart.
The anonymous Englishman is Charles Godwin, a landowner and struggling sheep farmer who can barely keep the creditors of his philandering father, Lord Clare, at bay. Charles's wife, Amy Godwin, is paralysed and catatonic from a horseriding accident. Amy's sister, Constance, runs the Godwin household.
Seven years after giving up her daughter, Elisabeth finds employment as the new governess for the child, who is named Louisa. Elisabeth knows that Louisa is her daughter. Initially, Charles Godwin rejects Elisabeth and demands that she leave immediately, but Constance asks him to give the new governess a month to find a new situation. He makes Elisabeth swear never to reveal to Louisa or anyone else the nature of their previous relationship.
Louisa is a spoiled, ignorant, and wilful child, loved by no one except her father. Elisabeth is appalled by the lack of discipline in the household, while Charles refuses to discipline the girl. Unable to keep Louisa at her lessons, Elisabeth locks the child in the classroom. When Charles discovers this, he is furious and roughly manhandles Elisabeth in an effort to obtain the key to the schoolroom. Elisabeth, while trying to guide Louisa toward a better path, promises that she will never harm the girl and that whatever she does to Louisa she will do to herself in return, intending to gain Charles’s support for her approach. During this time, Elisabeth also rejects a marriage proposal from an American rancher who is staying with Godwin.
Outside of class, Louisa spends all her spare time in the lakehouse, a small belvedere on the estate in the middle of a lake, reachable only by boat. Louisa pretends she has a mother. Elisabeth watches from the jetty at first, then starts visiting the lakehouse herself after discovering that Charles swims naked there in the mornings, though she leaves before he can see her. In the classroom, Elisabeth paints picture cards to teach the seven-year-old to read and tells Louisa a tale about the firelight, a storytelling device that helps her concentrate and gives her a sense of freedom from constant rules.
Eventually, Elisabeth and Charles grow increasingly drawn to each other and begin a sexual relationship. Charles even speaks of leaving everything behind to be together, but Elisabeth insists that such a path is impossible given his obligations to the estate, family, and his wife. Then Charles reveals that the entire estate is being appraised for sale to cover his mounting debts. On a bitterly cold night, he contemplates whether his wife would want to be freed from her catatonic prison and, in an act of conscience, opens her bedroom window, lets the fire go out, and allows her to die of exposure. Amy dies, and Constance acknowledges that she has grown close to Charles, though they cannot marry. At Amy’s funeral, Constance realises the depth of Charles’s feeling for Elisabeth, and Elisabeth confronts Charles, asking if he killed Amy; he admits it. They both feel guilt, but neither regrets what they have shared.
Soon after, Louisa discovers Elisabeth’s journal, which is dedicated to “My English Daughter.” Elisabeth confirms that Louisa is her daughter. After the sale of the Godwin estate, Charles, Elisabeth, and Louisa leave on a snowy day to begin a new life together as a family.
