The book opens with Stephen’s first impressions as a very small child; bits and pieces of children’s stories and songs, memories
of common household objects, and even remembered smells make up the stream-of-consciousness plot of the first few pages. The narration then shifts to Stephen’s early days at a Dublin public school, Clongowes. The events in this portion of the novel are recorded in no certain order: He is often teased by the older boys, he becomes ill and spends time in the school infirmary, he hears of the death of the Irish patriot Charles Parnell. During Christmas dinner back home, a political argument erupts among the members of the Dedalus family over the role of Ireland’s priesthood in the country’s struggle for independence. The chapter ends with further recollections of Stephen’s early school days and a session with the school’s headmaster in his study; Stephen’s eyeglasses have been accidentally broken, and he has been unfairly paddled by one of the teachers, Father Dolan. He relates the story to the headmaster, who promises to speak to Father Dolan and to right the wrong. Stephen becomes a school hero.
The Dedalus family is often forced to move owing to Simon Dedalus’ improvidence, a situation over which the older Stephen now feels great embarrassment. Chapter 2 also deals with the boy’s awakening sexuality. In love with a pretty girl at a children’s birthday party, Stephen is too shy to divulge his feelings to her. Stephen’s intelligence has won for him a scholarship to the prestigious Belvedere School, affording him the opportunity to have a first-class education. He submits a well-thought-out essay to his English master, who detects "heresy" in the essay’s central theme; the master points this out in class, and after school Stephen is beaten up by some of the other boys who are at once jealous of his intelligence and outraged by his nonconformity. Next Stephen stars in a school play; his dramatic success, his growing maturity, and the sense of his own intellectual superiority have made him more self-confident.
Accompanying his father to Cork, Stephen notes the older man’s vanity and begins to understand the kind of person his father is—carefree, charming, irresponsible. The second chapter concludes on a climactic note: Stephen wanders into Dublin’s red-light district, where he has his first sexual experience, with a prostitute.
At the beginning of the next chapter, Stephen’s experiences with prostitutes have become commonplace. Meanwhile, however, he is undergoing catechism for confirmation in the church; connected with this religious training is a "retreat" at which he and other boys spend time meditating and listening to a course of sermons by Father Arnall, an eloquent "fire-and-brimstone" preacher. The four sermons deal with the "last things," the crucial experiences surrounding the death of the believing Roman Catholic: death, judgment, Hell, and Heaven. Although Stephen has been heavily influenced by his "worldly" reading of poets and philosophers, making him cynical about his parents’ religious beliefs, the sermons grip his heart. He is wrung by remorse over his sexual sinning, but he feels far too lost for redemption. Eventually, he musters enough courage to confess to a priest his visits to prostitutes. As the chapter ends, Stephen feels cleansed and released from worldly burdens.
In chapter 4, Stephen has become definitely sanctimonious. He hits on the idea of becoming a priest, but his spiritual adviser suggests that he attend the Royal University in Dublin instead. Here his spiritual pride turns into intellectual and artistic egotism, and he spends long hours in self-reflection, often taking lengthy walks. During one such outing along Dublin’s seacoast, Stephen sees a girl about his own age wading in the surf, her shirt tucked up about her knees. She is quite pretty and he stares at her; she turns and looks directly into his eyes. The moment seems timeless to Stephen, but she finally turns away. Stephen is strangely moved by this encounter, which he takes as a visitation by "the angel of mortal youth and beauty," marking his entry into a new world of art and spiritual adventure.
In the last chapter, Stephen has become an intellectual and a poet. His friends now are his classmates at the university, and the contrast between his increasingly sordid family life (where Simon’s irresponsibility has led to outright poverty) and his successes at college cause him to chafe at the limits of his environment. Much of the chapter is taken up with several thematic strands, usually embodied in conversations with his classmates: the Irish nationalist movement, aesthetic philosophy, and alienation from England and the wider European tradition. Throughout the chapter, Stephen is composing a villanelle, a complex verse form, to his childhood sweetheart, the girl he was too shy to kiss in chapter two.
The novel closes with entries from Stephen’s diary, reflecting his impatience with Ireland’s backwardness and with the stagnation of his own life. At the book’s close, he resolves to move out into the wider world, "to forge in the smithy of
soul the uncreated conscience" of the Irish race.