Once the protagonist and Beauplaisir part ways in London, she rents rooms under the name of Widow Bloomer and sends word for him via letter to come and visit her there. Then she goes back to the rooms she rented as Fantomina and instructs the servants to make sure that if Beauplaisir comes looking for her, he is not told that she has been away from London. Disguising her handwriting, she sends him a letter lamenting that he has not come to see her, and attributes it to Fantomina.
Beauplaisir promptly responds to both letters, vowing his affection and fidelity to both women. The protagonist is outraged at his lies, but is relieved that she has protected herself, and decides to keep enjoying the sexual aspect of the relationship. Beauplaisir visits her both when she is the Widow and when she is Fantomina, and she notices that he strongly prefers the former, because that relationship is newer. However, within a fairly short time, Beauplaisir has also tired of the widow.
Fantomina now has a new scheme, and this one requires help. She finds two men and offers to pay them to render her some service. They happily agree and she arranges to meet them the following day. Then she goes to rent a large and splendid house. When she meets the two men she has hired, she presents them with uniforms resembling those worn by the servants of the wealthy. She tells one of them to deliver a letter to Beauplaisir. This letter has been written in a handwriting that is different from that of her other letters. It purports to be from an anonymous woman (signed Incognita) who is in love with him and wants him to come and visit her. She promises to do anything he wants, but insists that she will not reveal her name or face. The messenger has been instructed to refuse to give any details if Beauplaisir tries to find out her identity.
When the letter is delivered, Beauplaisir does indeed try to find out who Incognita is, but he is not given any information. With his curiosity inflamed, he writes back expressing his eagerness to meet this mysterious woman. The two meet at the house the protagonist rented, and she appears with a mask. They have sex, and then Beauplaisir begins to try to persuade her to show him her face. She refuses, and when he realizes she is not going to change her mind, he asks if he can spend the night at her house. The protagonist agrees, but is suspicious of what his motives are. She is right to be suspicious, as Beauplaisir plans to unmask her while she is sleeping. The protagonist ensures that she joins him in bed in a very dark room, and even when it grows light outside, the windows are so tightly sealed that no light penetrates the room. As soon as they awake, she hurries out of the room without his having seen her face. Frustrated, Beauplaisir expresses his unhappiness that she will not show him her face. However, the protagonist holds firm, and he leaves the house determined not to see her again.
Beauplaisir has already demonstrated his lack of constancy, but this section highlights his tendency towards outright deception. Rather than simply ending his relationships, he continues to deceive and string along whom he believes to be multiple women. This realization seems to validate the protagonist's suspicions and makes her happy that she has taken precautions to protect herself. However, knowing that Beauplaisir is willing to blatantly lie and be unfaithful to her does not make her want to sever contact with him. She hopes to continue to enjoy the sexual aspect of their relationship while being pragmatic about his failings. This decision on her part can be read as either empowered, or self-delusional. In one reading, she does not need his fidelity or even affection: she can assess the relative merits of the relationship, and so long as he continues to gratify her sexually, she can make a clear-eyed decision to keep him around. Alternatively, it can be argued that she is so infatuated with Beauplaisir that she simply continues to find excuses to pursue the relationship even though it offers her little benefit and no security.
Tricking and manipulating Beauplaisir also appears to have become something of an obsession for the heroine. It may enhance her sexual pleasure to know that she secretly has the upper hand, and that she can also set the terms of their encounters. Her disguise as Incognita is the most explicit form of trickery yet, in that here it is clear to Beauplaisir that information is being withheld from him and that he does not actually know the woman with whom he is interacting. This final disguise also generates a more explicit reversal of power. While the protagonist has of course stage-managed her previous encounters with Beauplaisir, to him they appeared as simple coincidences. Here, it is very obvious that the mysterious woman has summoned him for her own sexual gratification and is controlling the situation. It is also noted that here, for the first time, the protagonist does not even try to pretend to fend off his sexual overtures. In the disguise of Incognita, she can finally portray a woman who takes full ownership of her sexuality and dictates the terms of her encounters.
Beauplaisir's reaction to actually knowing he is being manipulated and deceived shows why the protagonist was right to pursue secrecy. He has no interest in respecting the boundaries Incognita sets, and immediately starts plotting to find a way to reveal her true identity. He ignores the fact that she has said she does not want to show him her face, just as he previously ignored Fantomina saying she did not want to have sex with him. When he realizes he has been outwitted, and that by making sure the room will remain totally dark, Incognita has ensured he will be unable to see her face, he reacts with frustration and anger. Ironically, considering the number of women with whom he thinks he is being dishonest, he expects total transparency from her, and is angry that she will not simply give in to his demands of revealing her identity.