Oliver Twist is the story of the titular orphan, Oliver, and his experiences as a foundling and, later, a criminal in Victorian London. Oliver begins his life in a workhouse administrated by the greedy and abusive Bumbles. Later he meets a burglar and pickpocket known as the Artful Dodger who introduces him to the crime boss Fagin. Oliver becomes involved in crime and leads a squalid, unpleasant life until finally being rescued by the charitable Mr. Brownhouse.
Oliver Twist was born into a life of poverty and misfortune in a workhouse in an unnamed town (although when originally published in Bentley's Miscellany in 1837, the town was called Mudfog and said to be within 70 miles north of London– in reality this is the location of the town of Northampton). Orphaned by his mother's death in childbirth and his father's unexplained absence, Oliver is meagrely provided for under the terms of the Poor Law and spends the first nine years of his life living at a baby farm in the 'care' of a woman named Mrs. Mann. Oliver is brought up with little food and few comforts. Around the time of Oliver's ninth birthday, Mr. Bumble, the parish beadle, removes Oliver from the baby farm and puts him to work picking and weaving oakum at the main workhouse. Oliver, who toils with very little food, remains in the workhouse for six months. One day, the desperately hungry boys decide to draw lots; the loser must ask for another portion of gruel. The task falls to Oliver, who at the next meal tremblingly comes up forward, bowl in hand, and begs Mr. Bumble for gruel with his famous request: "Please, sir, I want some more".
A great uproar ensues. The board of well-fed gentlemen who administer the workhouse hypocritically offer£5 to any person wishing to take on the boy as an apprentice. Mr. Gamfield, a brutal chimney sweep, almost claims Oliver. However, when he begs despairingly not to be sent away with "that dreadful man", a kindly old magistrate refuses to sign the indentures. Later, Mr. Sowerberry, an undertaker employed by the parish, takes Oliver into his service. He treats Oliver better and, because of the boy's sorrowful countenance, uses him as a mourner at children's funerals. However, Mr. Sowerberry is in an unhappy marriage, and his wife takes an immediate dislike to Oliver – primarily because her husband seems to like him – and loses few opportunities to underfeed and mistreat him. He also suffers torment at the hands of Noah Claypole, an oafish but bullying fellow apprentice and "charity boy" who is jealous of Oliver's promotion to mute, and Charlotte, the Sowerberrys' maidservant, who is in love with Noah.
In trying to bait Oliver, Noah insults Oliver's biological mother, calling her "a regular right-down bad 'un". Oliver flies into a rage, attacking and beating the much bigger boy. Mrs. Sowerberry takes Noah's side, helps him to subdue, punch, and beat Oliver, and later compels her husband and Mr. Bumble, who has been sent for in the aftermath of the fight, to beat Oliver once again. Once Oliver is sent to his room for the night, he breaks down and weeps, upset at the events which he had faced. The next day, Oliver escapes from the Sowerberrys' house and decides to run away to London instead.
During his journey to London, Oliver encounters Jack Dawkins, a pickpocket more commonly known by the nickname the "Artful Dodger", and his sidekick, a boy of a humorous nature, named Charley Bates, but Oliver's innocent nature prevents him from recognizing any hint that the boys may be dishonest. Dodger provides Oliver with a free meal and tells him of a gentleman in London who will "give him lodgings for nothing, and never ask for change". Grateful for the unexpected assistance, Oliver follows Dodger to the "old gentleman's" residence. In this way, Oliver unwittingly falls in with an infamous Jewish criminal known as Fagin, the so-called gentleman of whom the Artful Dodger spoke. Ensnared, Oliver lives with Fagin and his gang of juvenile pickpockets in their lair at Saffron Hill for some time, unaware of their criminal occupations. He believes they make wallets and handkerchiefs.
Later, Oliver naïvely goes out to "make handkerchiefs" (because there is no income) with the Artful Dodger and Charley Bates. Oliver realises too late that their real mission is to pick pockets. Dodger and Charley steal the handkerchief of an old gentleman named Mr. Brownlow, and promptly flee. When he finds his handkerchief missing, Mr. Brownlow turns round, sees Oliver running away in fright, and pursues him. Others join the chase and Oliver is caught and taken before the magistrate. Curiously, Mr. Brownlow has second thoughts about the boy – he seems reluctant to believe he is a pickpocket. To the judge's evident disappointment, a bookstall holder who saw Dodger commit the crime clears Oliver, who, by now actually ill, faints in the courtroom. Mr. Brownlow takes Oliver home and, along with his housekeeper Mrs. Bedwin, cares for him.
Oliver stays with Mr. Brownlow, recovers rapidly, and blossoms from the unaccustomed kindness. His bliss, however, is interrupted when Fagin, fearing Oliver might "peach" on his criminal gang, decides that Oliver must be brought back to his hideout. When Mr. Brownlow sends Oliver out to pay for some books, one of the gang, a young girl named Nancy, whom Oliver had previously met at Fagin's, accosts him with help from her abusive lover, a brutal robber named Bill Sikes, and Oliver is quickly bundled back to Fagin's lair. The thieves take the five-pound note Mr. Brownlow had entrusted to him, and strip him of his fine new clothes. Oliver, dismayed, flees and attempts to call for police assistance, but is ruthlessly dragged back by the Artful Dodger, Charley and Fagin. Nancy, however, is sympathetic towards Oliver and saves him from beatings by Fagin and Sikes.
In a renewed attempt to draw Oliver into a life of crime, Fagin forces him to participate in a burglary. Nancy reluctantly assists in recruiting him, all the while assuring the boy that she will help him if she can. Sikes, after threatening to kill him if he does not cooperate, sends Oliver through a small window and orders him to unlock the front door. The robbery goes wrong, however, and Oliver is shot and wounded in his left arm at the targeted house. After being abandoned by Sikes, the wounded Oliver makes it back to the house and ends up under the care of the people he was supposed to rob: Miss Rose and her guardian Mrs. Maylie.
A mysterious man named Monks has found Fagin and is plotting with him to destroy Oliver's reputation. Monks denounces Fagin's failure to turn Oliver into a criminal, and the two of them agree on a plan to make sure he does not find out about his past. Monks is apparently related to Oliver in some way, although this is not mentioned until later. Back in Oliver's home town, Mr. Bumble has married Mrs. Corney, the wealthy matron of the workhouse where the story first began, only to find himself in an unhappy marriage, constantly arguing with his domineering wife. After one such argument, Mr. Bumble walks over to a pub, where he meets Monks, who questions him about Oliver. Bumble informs Monks that he knows someone who can give Monks more information for a price, and later Monks meets secretly with the Bumbles. After Mrs. Bumble has told Monks all she knows, the three arrange to take a locket and ring which had once belonged to Oliver's mother and toss them into a nearby river. Monks relates this to Fagin as part of the plot to destroy Oliver, unaware that Nancy has eavesdropped on their conversation and gone ahead to inform Oliver's benefactors.
Now ashamed of her role in Oliver's kidnapping and fearful for the boy's safety, Nancy goes to Rose Maylie and Mr. Brownlow to warn them. She knows that Monks and Fagin are plotting to get their hands on the boy again and holds some secret meetings on the subject with Oliver's benefactors. One night, Nancy tries to leave for one of the meetings, but Sikes refuses permission when she declines to state exactly she is going. Fagin realises that Nancy is up to something and resolves to find out what her secret is. Meanwhile, Noah has fallen out with the undertaker Mr. Sowerberry, stolen money from him, and fled to London. Charlotte has accompanied him— they are now in a relationship. Using the name "Morris Bolter", he joins Fagin's gang for protection and becomes a practicer of "the kinchin lay" (kidnapping of children), and Charlotte (it is implied) becomes a prostitute. During Noah's stay with Fagin, the Artful Dodger is caught with a stolensilver snuff box, convicted (in a very humorous courtroom scene), and transported to Australia. Later, Noah is sent by Fagin to "dodge" (spy on) Nancy, and discovers her secret: she has been meeting secretly with Rose and Mr. Brownlow to discuss how to save Oliver from Fagin and Monks.
Fagin angrily passes the information on to Sikes, twisting the story just enough to make it sound as if Nancy had informed on him. Believing Nancy to be a traitor, Sikes beats her to death in a fit of rage and flees to the countryside to escape from the police. There, Sikes is haunted by visions of Nancy's ghost and increasingly alarmed by news of her murder spreading across the countryside. He returns to London to find a hiding place, only to die by accidentally hanging himself while attempting to flee across a rooftop from an angry mob.
Monks is forced by Mr. Brownlow to divulge his secrets: his real name is Edward Leeford, and he is Oliver's paternal half-brother and, although he is legitimate, he was born of a loveless marriage. Oliver's mother, Agnes, became their father's true love after Monks witnessed his parents' divorce. Mr. Brownlow has a picture of Agnes, and began making inquiries when he noticed a marked resemblance between her and Oliver. Monks has spent many years searching for his father's child– not to befriend him, but to destroy him (see Henry Fielding's Tom Jones for similar circumstances). Brownlow asks Oliver to give half his inheritance (which proves to be meagre) to Monks because he wants to give him a second chance; and Oliver, being prone to giving second chances, is more than happy to comply. Monks later moves to America, where he squanders his money, reverts to crime, and ultimately dies in prison. Fagin is arrested and condemned to the gallows. On the eve of his hanging, in an emotional scene, Oliver, accompanied by Mr. Brownlow, goes to visit the old reprobate in Newgate Gaol, where Fagin's terror at being hanged has caused him to lose himself in daydreams and develop a fever.
On a happier note, Rose Maylie turns out to be the long-lost sister of Agnes, and therefore Oliver's aunt. She marries her long-time sweetheart Harry, and Oliver lives happily with his saviour, Mr. Brownlow. Noah becomes a paid, semi-professional police informer. The Bumbles lose their jobs and are reduced to great poverty, eventually ending up in the same workhouse where they originally lorded it over Oliver and the other orphan boys. Charley Bates, horrified by Sikes's murder of Nancy, becomes an honest citizen, moves to the country, and works his way up to prosperity.