The narrator disagrees with "Moral Writers" who believe that virtue leads to happiness and vice to grief.
Lord Fellamar, a nobleman who brought Sophia home from the play, is a frequent visitor at Lady Bellaston's house. He has fallen in love with Sophia. One morning he visits Sophia for two hours before realizing that he has stayed too long. Lady Bellaston is pleased with Fellamar's lengthy visit—she is hoping to deflect Sophia from Tom through Fellamar. Lady Bellaston advertises Sophia to Fellamar by telling him about her great fortune. She complains, however, that Sophia is in love with "one of the lowest Fellows in the World a Beggar, a Bastard, a Foundling." She invites Fellamar to dine with them the following day so that she can prove to him that Sophia is attached to such a man.
Lady Bellaston is a member of the "Little World," a high-class club. She devises a plan for the dinner that night with Fellamar and calls on the assistance of Edwards, another member of the club. Specifically, Edwards has to say that a certain Colonel Wilcox was killed by Tom Jones in a duel. Sophia faints on hearing the news, proving to Fellamar that Lady Bellaston was correct in her assertions about Sophia's love for Tom. Lady Bellaston contrives to have Fellamar and Sophia meet at seven the following evening. She has secretly been encouraging Fellamar to rape Sophia so that Sophia will be obliged to marry him. Fellamar is tortured by the thought of the crime, and resolves that his "Honour" will subdue his "Appetite." The following day Sophia begs Lady Bellaston not to admit Fellamar. Her aunt chastises her, and snides that country girls think every man who is courteous to them intends to make love to them.
Lady Bellaston distorts literary examples of rape to try to convince Fellamar to ravish Sophia. It is ultimately for Sophia's good, she argues, since Fellamar will be a fine husband for her. Fellamar agrees to carry through with Lady Bellaston's plan, extolling Sophia's beauty and fortune.
Lord Fellamar enters Sophia's room and throws himself at her feet, offering her the world. She rejects him in harsh terms. He grabs hold of her and she screams out, but Lady Bellaston has removed everyone from earshot. At this moment Sophia hears her father's voice as he thunders up the stairs. She calls out to her father, and Fellamar releases her. Squire Western explodes into the room, drunk and verbally abusive. Western orders Sophia to marry Blifil. Fellamar thinks that Western is speaking of him, and thanks him for the honor of considering him as his son-in-law. Western curses Fellamar, who departs as quickly as possible. Lady Bellaston chastises Western for his rudeness to so great a man. Western declares that he wants a country man, not a city fop, for Sophia. He violently drags his daughter down to his coach, swearing to lock her up.
Mrs. Fitzpatrick is the one who betrayed Sophia's whereabouts to Squire Western and Mrs. Western. The narrator presents her fawning, obsequient letter to Mrs. Western.
At Mrs. Miller's house, Mrs. Honour laments losing Sophia. Jones, thinking that Sophia must have died, frantically begs Honour to tell him what has happened. When Jones finally extracts the news that Western has locked up Sophia and dismissed Honour, Tom is thankful that Sophia is alive. Honour chides Jones for not having compassion for her misfortune, since she says that she has always taken his part against Blifil. Honour is scared that Western will hurt Sophia. She says she wishes Sophia had some of her courage—if her father withheld her from the man she loved, she would tear out his eyes. Partridge runs into the room to inform Jones that Lady Bellaston has arrived. Jones hides Honour behind the bed. Lady Bellaston plops herself on the bed and scolds Jones for not contacting her. Then she flirts with him. Lady Bellaston waits in surprise as Jones stands awkwardly, not knowing what to do. A very drunk Nightingale suddenly bursts into Tom's room, mistaking it for his own. Partridge manages to lead Nightingale away. While Tom was occupied with Nightingale, Lady Bellaston tried to hide herself behind the bed, coming face to face with Honour. The ladies are horrified. Lady Bellaston implies that she will bribe Mrs. Honour, after which Honour calms down. Lady Bellaston leaves, shunning Tom's attempts to hold her hand. Honour is upset about Tom's infidelity to Sophia, but Tom "at last found means to reconcile her."
Mrs. Miller gently scolds Tom for the upheaval in his room the previous night. Nightingale and Nancy are married that day, with Tom acting as father to Nancy. Before the wedding, Nightingale's uncle tries to intoxicate him and dissuade him from marrying Nancy. News arrives during this meeting that Harriet, the daughter of Nightingale's uncle, has run away with a neighboring clergyman. This destroys his case with Nightingale.
Tom receives three letters from Lady Bellaston summoning him immediately. Nightingale enters the room while Tom is reading and reveals that he knows about Tom's affair with Lady Bellaston. Tom asks for more details on the affairs of Lady Bellaston, but the narrator refuses to repeat Nightingale's words for fear of being accused of spreading scandals.
Nightingale's stories greatly reduce Tom's gratitude to Lady Bellaston and he realizes that he has been in "commerce" with this lady rather than in "love." Nightingale advises Jones that the easiest way for him to rid himself of Lady Bellaston is by proposing marriage. Together they compose a letter of proposal, to which Lady Bellaston replies that she is offended that Tom is so covetous of her fortune. Tom responds that he is insulted by her suspicion and will return her gifts to him. At the wedding dinner that night, Mrs. Miller devotes more attention to Tom than to Nightingale and Nancy.
Mrs. Miller has received a letter from Allworthy informing her that he and Blifil are coming immediately to London. He wishes to reserve the first and second floors of her house. The truth is that when Allworthy started paying Mrs. Miller an annuity of fifty pounds, it was on condition that he could occupy the first floor of her house whenever he came to town. Mrs. Miller thus has to comply with Allworthy's wishes, but she is distressed that Jones and Nightingale have to leave. Jones says that he does not mind at all. Honour sends Jones a letter saying that she is sure he will attain Sophia in the end, but she can no longer be of service to him. Lady Bellaston has hired her.
Mrs. Arabella Hunt, a friend of Mrs. Miller's, sends Tom a marriage proposal. She is twenty-six and a little plump, but otherwise attractive. She has recently been widowed by a turkey merchant who left her a rich woman. Tom is at first excited by the prospect of having so much money, but—thinking of Sophia—writes a courteous refusal.
Partridge capers into Jones's room with good tidings. He has found out that Black George is now a servant in Squire Western's apartment in London, by which means Tom may send letters to Sophia. Much to Tom's frustration, however, Partridge cannot remember the name of the street on which Western lives.
Book XV reveals the extent of Lady Bellaston's wickedness when she attempts to convince Lord Fellamar to rape Sophia. Fielding prevents the reader from seeing the "rape scene" in a tragic light, however, by the manner in which he describes it. Fielding further achieves this by including Lady Bellaston's humorous distortions of Classical literary descriptions of rape in Chapter IV. Fielding makes fun of many characters on the basis of their poor Classical knowledge—such as Partridge, and literary critics.
The introduction of Lord Fellamar, first as a nameless gentleman who takes Sophia home from a play and then as a suitor, is indicative of Fielding's characterization method throughout the novel—he often withholds characters' names until a few chapters after their introduction. This delay is perhaps intended to rouse the reader's analytical energies—indeed, the narrator urges his reader not to be lazy, but to constantly interpret characters' words and actions for themselves. Fielding often provides an explanation or analysis himself, but always after some delay. For example, in Chapter III Fielding first praises Lady Bellaston's "Little World Society" as "an honourable Club," but a couple of paragraphs later refers to it as a "comical Society."
The behavior of Squire Western deserves some attention in this book, as his rejection of Lord Fellamar stems not only from his conservative nature, but also from his loyalty to the country and to tradition. The fact that Western is not simply ravenous for the status and riches Lord Fellamar would bring to his family, as is Mrs. Western, allows the reader to grant him some integrity.