The first word of spoken dialogue is, "Please, sir, I want some more."
Oliver is an orphan chosen by his messmates to ask for a second helping of gruel, as all the boys are kept continuously hungry while those who run the workhouse eat lavishly. For this effrontery he is punished with expulsion, sold like a slave to an undertaker. After a fight with an apprentice, he runs away to London, a 7 day journey by foot.
In London he meets the Artful Dodger, an experienced pickpocket, who brings him to Fagin, master pickpocket who maintains a pack of boy pickpockets. Fagin also fences stolen goods for for the likes of Bill Sikes.
Comparison with the novel
The plot is considerably simplified, with many of the characters losing much of their original depth (such as Fagin, who becomes considerably more comedic in the musical and loses much of his original darker side.) Some characters, such as Oliver's brother Monks, are removed entirely.