The vicious divorce of the socialites Ida and Beale Farange ends in a split-custody agreement over their daughter, Maisie. Maisie begins with her father, Beale, but struggles to adjust to life as a child of divorce, especially as her parents continue to use her to hurt each other. Maisie pretends to be stupid to avoid their attention and criticism.
Moving to Ida’s, Maisie develops a close relationship with her new governess, Miss Overmore. Ida forbids Miss Overmore from going back to Beale’s with Maisie, but Miss Overmore disobeys her and becomes Maisie’s governess when she is with Beale instead. Back at Ida’s, Maisie has a new governess: the elderly Mrs. Wix. Mrs. Wix at first frightens Maisie, but they soon develop a strong bond, despite Mrs. Wix’s limited qualifications as a governess. Returning to Beale’s, Maisie senses intrigue. Eventually, Mrs. Wix comes to see her and explains that Ida is going to marry a man named Sir Claude. A confrontation between Mrs. Wix and Miss Overmore reveals that Miss Overmore and Beale also just married—Maisie is instructed to call Miss Overmore Mrs. Beale from now on. As her new stepmother, Mrs. Beale will no longer be Maisie’s governess.
Sir Claude comes to bring Maisie back to Ida’s, and Maisie observes the instant rapport he has with Mrs. Beale. Maisie is reunited with Mrs. Wix but finds Ida to be cold and distant or unpredictable and aggressive. Maisie becomes close with Sir Claude, who is increasingly the main target of Ida’s anger. Sir Claude is unbothered, however, and continues to stick up for Maisie and Mrs. Wix. Maisie learns that Sir Claude has been having an affair with Mrs. Beale, which greatly upsets Mrs. Wix.
Back at Beale’s, Maisie finds her stepmother transformed into a socialite too. Sir Claude visits her, and on one outing they run into Ida and her new lover, the Captain, prompting a vicious confrontation between Ida and Sir Claude. Later, Mrs. Beale takes Maisie out to an Exhibition, where they see Beale out with his new mistress. Beale grabs Maisie and takes her to his mistress’s house, explaining that he and the Countess are going to America. He halfheartedly invites Maisie along, but she declines.
Sir Claude visits Maisie again and abruptly tells her to pack her things—he is taking her to France, away from her broken family. For his part, Sir Claude is also running away from the women in his life, as his relationships with Ida and Mrs. Beale are both strained. On the Channel coast, before crossing to France, Maisie and Sir Claude are confronted by Ida, who learned of their trip. Ida does not try to stop them, however, and seems relieved to have Maisie taken off of her hands—and is increasingly mentally unwell herself.
Maisie and Sir Claude cross the Channel to France but do not continue onward to Paris. Instead, they wait for Mrs. Wix, whom Ida has sent to join them. Ida doesn’t want Maisie cared for by Beale’s maid Susan Ash, whom Sir Claude brought along. Ida has broken off her relationship with Sir Claude, leaving him free to do as he pleases. Soon a letter arrives from Mrs. Beale, revealing that Beale too has left her for the Countess. Sir Claude is excited to learn that he and Mrs. Beale are free to be together, but Mrs. Wix contradicts him, insisting that under the circumstances—they are both still married, if in name only—their affair remains immoral and inappropriate to involve Maisie in. Sir Claude dismisses her and takes Susan Ash back to England, presumably as an excuse to see Mrs. Beale.
Left in France with Mrs. Wix, Maisie takes in the sights but also argues with her governess, as she is unable to understand why Mrs. Wix is so attached to social norms of morality and unwilling to accept Sir Claude and Mrs. Beale’s relationship. Mrs. Wix insists she is trying to protect Maisie and give her some kind of moral education, something that all of her corrupted parents are unwilling or unable to do. Maisie and Mrs. Wix are surprised by the arrival of Mrs. Beale, without Sir Claude. Mrs. Beale’s attitude toward Mrs. Wix is transformed. She flatters her with attention in order to have the governess on her side, not Sir Claude’s, revealing her intention to use Maisie—with Ida and Beale gone, Sir Claude and Mrs. Beale now have custody—to force Sir Claude to stay with her. This suggests to Maisie that Mrs. Wix has influenced Sir Claude, who is feeling conflicted about his relationship with Mrs. Beale.
Sir Claude returns visibly anxious and takes Maisie out for breakfast. He offers Maisie a choice: she can stay with him and Mrs. Beale, but only if they fire Mrs. Wix, who will never accept their affair. Maisie asks for time to consider, and she and Sir Claude spend the day out and about as she wrestles with the decision. They go to the train station to buy newspapers, and in a flight of fancy almost get on the train to Paris, but it leaves before Maisie can make up her mind. Maisie then makes a counteroffer to Sir Claude: for him to leave Mrs. Beale and come with her and Mrs. Wix. Eventually they return to the hotel, where they find Mrs. Wix about to leave and Mrs. Beale in a state of distress. A full-on confrontation ensues, and Mrs. Wix offers Maisie her own choice: to come with her and leave Sir Claude and Mrs. Beale. Sir Claude defends Maisie’s right to make her own decision against Mrs. Beale’s furious anger, but he remains unable to stand up for himself or to resist Mrs. Beale. Dismayed but forced to decide, Maisie chooses Mrs. Wix, and the two of them leave the unhappy couple and return to England.