The following day, the heroine drives with Beatrice to visit Gran, the aged grandmother of Maxim and Beatrice. Along the way, her sister-in-law tells her that Jack Favell was Rebecca's cousin, and that he visited Manderley frequently while she was alive. Gran is nearly blind and terribly forgetful, and yet the visit goes well at first--until the old lady suddenly starts demanding to see Rebecca: "Why did not Maxim bring Rebecca?" she asks. "I'm so fond of Rebecca. Where is dear Rebecca?" Beatrice, mortified, takes the heroine away at once. When she returns to Manderley, the heroine finds that Maxim has arrived back London; coming in, she overhears him speaking to Mrs. Danvers, angrily forbidding Jack Favell from coming to his home again.
A few weeks later, on a Sunday, Maxim and the heroine are hosting guests at Manderley, and one of them, a Lady Crowan, asks if they will be holding a costume ball, which was apparently a yearly tradition at Manderley when Rebecca was alive. After much discussion, Maxim agrees to host the event, and Frank Crawley promises to work with Mrs. Danvers on the preparations. It will be the heroine's first grand affair as mistress of Manderley, and almost in spite of herself she begins to feel excited. While she tries to decide what to wear, none other than Mrs. Danvers comes to see her, with a suggestion for her costume: she advises her to take as her model one of the huge, 18th-century paintings that hang in the stairwell, showing a lovely young woman holding her hat in her hand. She even goes so far as to suggest an excellent dressmaker in London that would take the commission. The heroine is astonished by this behavior, and decides that perhaps Mrs. Danvers has finally decided to be friendly. After thinking carefully on the matter, she resolves to follow the housekeeper's advice, and to order a costume like the one worn by the woman in the painting.
As the day of the ball approaches, she conceals from everyone the details of her planned costume, hoping to surprise them. On the night of the festivities, Giles and Beatrice arrive early, and they chat with Frank Crawley and Maxim while the heroine goes upstairs to change, with Clarice's assistance. She comes down the main staircase grandly, confident that they will all be stunned by her appearance. They are, but not in the way she imagined: Maxim turns white, and orders her to go upstairs and change back out of the dress. Bewildered and hurt, she returns to her room and breaks down in tears. Beatrice follows her, and explains why they were all so shocked: the heroine is wearing the same dress that Rebecca wore at her last costume ball. She tells her that Maxim believes she has done it on purpose.
A long time passes before the heroine can bring herself to go downstairs. The party is in full swing by then, and to explain the heroine's absence, as well as her present lack of costume, the guests have been told that the dressmaker had sent her the wrong costume. Somehow she survives the evening, wearing a simple dress and making idle conversation, all the while imagining that people are talking about her behind her back. The ball concludes with a fireworks display on the lawn, and the guests depart. The heroine goes to bed, tired and unhappy, and lies awake all night, waiting for her husband. But Maxim does not come.
The heroine's decision to follow Mrs. Danvers's advice, and dress as the lady in the painting, marks a key moment in the novel's psychological drama. (It is also a moment when the reader wonders how, after all the housekeeper's sinister behavior, the heroine could possibly trust her.) Ever since her arrival at Manderley, the heroine has failed to carve out her own identity as Mrs. de Winter; instead, she has allowed herself to be overcome by the palpable presence of the dead Rebecca, who has maintained her hold as mistress of Manderley from beyond the grave. The costume ball, the first large-scale public event at the mansion since her marriage, finally offers the heroine a chance to shine as herself, to carve out her own role as a hostess, and as a wife. But the evening ends in disaster.
By following the housekeeper's advice in her choice of costume, the heroine believes herself to be original, daring, surprising--to be making an impression, making her mark. In fact, however, her choice of costume comes from Mrs. Danvers, and thus ultimately from Rebecca. Ironically, instead of taking a step forward, separating herself from the specter of Maxim's dead wife, the heroine garbs herself in Rebecca's clothes, and walks in her footsteps. "You stood there on the stairs," Beatrice says afterward, "and for one ghastly moment I thought..." She trails off, leaving the thought unspoken, but her meaning is clear: she thought that Rebecca had come back to life. But thanks to Mrs. Danvers, and the heroine's own weakness, Rebecca is alive, and her identity at Manderley remains stronger than that of the present mistress.