The narrator prides himself on being the founder of "prosai-comi-epic Writing." He explains that the chapters that preface every book are meant philosophical and historical treatises. He then turns his focus on "critics," to whom he believes have received such authority that they think they can create rules for authors. The rules that critics have attempted to instigate, however, only "curb and restrain Genius." Returning to his prefacing remarks, the narrator explains that the introductory chapters are also intended to provide contrast: in their seriousness, they should excite the reader to reach the comic parts.
While Tom is in confinement because of his broken arm, Mr. Allworthy visits him every day and tries to make him deliberate on his misconduct. Thwackum often visits Tom to deliver dictatorial speeches out of his "duty" to urge reprobates, such as Tom, to repent. Thwacker says that Tom's broken arm is God's punishment for his sins. Square lectures Tom in a similar manner, but argues instead that a broken arm is nothing in the grand universal scheme. Blifil rarely visits, saying that he is scared to sully his character by spending time with Tom. Squire Western leaves Tom's room only to drink or hunt, while Sophia struggles to make herself stay at bay.
One day, while Tom and Squire Western listen to Sophia playing the harpsichord, Tom tells Western that, since his broken arm saved Sophia, he thinks of it as "the happiest Accident" of his life. Western wants to give Tom one of his horses as a reward. Sophia begins to play very badly, in such a way that Tom notices that something is bothering Sophia, and begins to suspect that she might be attracted to him.
Tom's love for Sophia is "bittersweet," since he is not completely sure that he has won her affection. Moreover, knowing that fortune and status are of fundamental importance to parents, Tom anticipates that Squire Western prohibit a marriage between him and Sophia. He does not want to abuse Western's hospitality to him, nor does he desire to offend Allworthy. Tom also thinks of Molly, to whom he has made promises of "eternal Constancy." He cannot bear to reflect on the image of Molly dying, which she has sworn to do if Tom deserts her. Molly's poverty has not once represented an obstacle to Tom. After a sleepless night, Tom resolves to remain faithful to Molly.
Mrs. Honour visits Tom on his sick-bed. She was deserted after being fooled by a nobleman's footman, and has never trusted another man with her heart, but she still loves men. Mrs. Honour tells Tom that Sophia has sent her to check on Molly, and Tom begs her for any information on Sophia. After a good deal of wheedling, Honour reveals that Sophia will not buy a new muff, but holds on to the one that Tom had kissed earlier. Squire Western enters to summon Tom to the harpsichord, where Sophia sits, wearing her muff and looking lovelier than ever. While Sophia is performing one of her father's favorite songs, the muff falls onto her fingers and prevents her from playing properly. Enraged, Western throws the muff into the fire, but Sophia immediately retrieves it from the flames.
Tom cannot get Molly out of his mind, and his compassion for her makes him overlook the fact that Sophia eclipses Molly in both appearance and character. Tom hopes that maybe he can apologize to Molly by offering her money, since her desperation might be greater than her love for him. One day, with his broken arm in a sling, Tom goes to visit Molly. Tom finds the upstairs door locked, and Molly eventually appears and tells Tom she has been sleeping. Tom tells Molly that Allworthy would be furious if he knew they were together, and says he wants Molly to find a man with whom she can lead a reputable life. She bursts into tears and accuses him of ruining and deserting her.
Suddenly, a rug that Molly has hung up to cover her clothes closet falls down, revealing Square. The narrator then tells the story of how Square and Molly came to be together. Square could not help noticing her beauty at church, and when he heard that her "Fortress of Virtue had already been subdued" by Tom, he felt perfectly justified in usurping Tom's place. Indeed, Square relishes the fact that Molly's lack of chastity allows him to have his way with her. Tom bursts into laughter and helps Square out of the cupboard. Square says that Tom cannot blame him for "corrupting Innocence," and Tom assures Square that he will keep the discovery a secret. Square agrees with Tom that sexual desire evolves out of a healthy natural appetite. Tom tells Molly that not only will he forgive her, but he will continue to assist her as much as he can. After Tom leaves, Molly chastises Square for being the reason she has lost Tom, but Square's caresses and his money restore Molly's devotion to him.
Jones worries that he has set Molly off on a course of debauched behavior, but Betty, Molly's eldest sister, assures Tom that a certain Will Barnes deserves that blame. Moreover, the child could just as easily belong to Will as Tom. Now Tom can turn his thoughts to Sophia, whom he loves. Tom cannot conceal his awkwardness in front of Sophia, and he has become unusually quiet and shy in her company. Western does not notice, but Sophia does, and she happily realizes the reason. One day, the two of them chance to cross paths in the garden. They meet suddenly and stroll together. When they arrive at the tree that Jones climbed to catch Sophia the bird when they were children, Sophia reminds him of the incident. She suspects that the memory must be emotional for him since he risked his life. Tom says he wishes he had died that day so he would not have to deal with the heartache of loving Sophia. Sophia, trembling, says that she must leave, but she stays to hear all that Tom has to say. They "totter" back together, hand in hand, with Sophia admonishing Jones not to say anything more on the matter. The narrator warns us that Jones must now face some bad news.
Tom has stayed with Western for two weeks without visiting Allworthy once, and in this time, Allworthy has fallen dangerously ill. Quoting the words of the Latin poet Cato, the narrator praises Allworthy for being calm in the face of death. He has no fears since he has lived an honest life. Allworthy summons his family to him and Tom races home, forgetting all thoughts of love.
At the bed, Blifil starts to cry and Allworthy delivers a long speech about the inevitability of death. He outlines the contents of his will to ascertain whether all are satisfied with their lot. The estate is to go to Blifil, with a smaller estate of 500 pounds a year set aside for Tom. In addition, Tom is to receive a flat sum of 1000 pounds. Tom throws himself at Allworthy's feet, thanking him for his generosity but insisting that he cannot think of anything as long as Allworthy's health lies in danger. Thwackum and Square are each to receive 1000 pounds and Allworthy has also made provisions for his servants. An attorney from Salisbury arrives and Allworthy composes himself to die.
Mrs. Wilkins launches on a long tirade about how she should not be grouped with the other servants in her master's will, and Thwackum and Square are not pleased with their inheritance either. Blifil returns from speaking to the attorney, from whom he has discovered that his mother has died from gout. Thwackum tells Blifil to bear the news like a "Christian" while Square tells him to bear it like a "Man." Blifil assures his tutors that he would not be able to survive if he did not have their sound lessons to fall back on. They debate whether or not to tell Allworthy about the death of his sister or not. In the sick room, the doctor declares that a miracle has occurred, and that Allworthy has recovered completely. The narrator lets the reader know that the situation was not actually as bad as the doctor had represented it. Blifil tells Allworthy about Bridget's death and Allworthy commissions Blifil to arrange the funeral.
Tom remains with Allworthy, consternated by his illness. The doctor assures the family that Allworthy's state has improved and that he will survive. Delighted at this report, Tom gets drunk, and the doctor has to quell a fight between Tom and Thwackum. Blifil, who detests Tom's unruly behavior since it is so different from his own, retorts that Tom should not behave in such a way when his mother has just died. Tom begs Blifil's pardon, but Blifil sneers that Tom cannot understand the pain of a parent's death since he does not even know who his parents were. Thwackum and the doctor have to stop Tom and Blifil from fighting.
On a beautiful June evening, Tom walks into a grove where nightingales are singing and breezes are fluttering the leaves. Alone, he meditates aloud on the beauty and charms of Sophia and swears eternal constancy to her. Suddenly Molly emerges from the brush and, after a brief conversation, Tom and Molly disappear together into the densest section of the grove. Thwackum and Blifil walk into this same grove and pursue Tom and his woman.
Tom is like a wild beast defending his mate. Thwackum swears he will track down the guilty woman, but Tom restrains him. The three men begin to fight, and are eventually joined by a "fourth Pair of Fists" that belong to Squire Western, who takes Tom's side. Tom and Western win the battle.
Sophia and Mrs. Western arrive at the scene of combat. Everyone rushes to help Blifil, who appears dead, but Sophia's fainting distracts them. Tom grasps Sophia in his arms and revives her in a brook. Western is so pleased with Tom for saving Sophia's life that he offers to give anything—except, of course, Sophia or his estate. Sophia sighs on seeing Tom's bruises from the brawl, and these sighs send Tom into a state of rapture. The narrator philosophizes on war, and wishes that all people could resolve disputes with their fists instead of with unnatural weapons. Thwackum tells Western what initiated the fight and Western chuckles, calling Tom a "liquorish Dog." Sophia, on the cusp of fainting again, begs to be taken home.
Allworthy's illness and the other characters' reaction to it makes the core of Book V, as does Tom's burgeoning love for Sophia. Tom's genuine concern for his benefactor contrasts with the selfish, pecuniary desires of Mrs. Wilkins, Thwackum, and Square, who shamelessly voice their disappointment over their inheritances. Of Mrs. Wilkins, the narrator observes that "Much more of the like Kind she muttered to herself; but this Taste shall suffice to the Reader." In such a way, the narrator places himself as a mediator between the reader and the world of his characters.
Thwackum and Square attempt to justify their anger through their religious and philosophical doctrines. Indeed, Thwackum and Square are indivisible—as a pair they highlight Fielding's claim that philosophy resting in theory alone signifies nothing. Thwackum and Square's views cancel each other out—by combining their theories, one can justify any behavior in the world. Fielding subtly implies that virtue stems from action rather than theory. Tom fits the bill of the "action hero", coming to Sophia's rescue twice. Tom's only fault is that he does not have moderation—as Allworthy advises him, he needs to learn "Prudence and Religion." Yet Tom's excessive behavior may be condoned, Fielding implies, since it is not born out of malice.
War imagery—in relation to love, disease, and domestic fighting—dominates Book V. In Chapter IV, Jones's realization of his love for Sophia is described as follows: "the Citadel of Jones was now taken by Surprize. the God of Love marched in in Triumph." In Chapter VII, the narrator philosophizes that a "Doctor and the Disease [should] meet in fair and equal Conflict by giving Time to the latter, we often suffer him to fortify and entrench himself, like a French Army." In such a manner, Fielding parodies domestic struggles by comparing them to national struggles.