The novel’s first scene shows an infant Stephen listening to his father’s nonsense fairy tale. Stephen’s thoughts and memories careen wildly – from a woman that sells candy on the street, to his mother’s warm smell, to his governess Dante’s brushes, to his neighbor Eileen. In the next scene, an older Stephen is in his first year of school at Clongowes; he is playing outside with the other boys and longing for the warmth and peace of study hall. He wakes up with a cold the next day and spends some time in the infirmary, where he hears that the Irish nationalist Parnell has died.
A few months later, Stephen comes home for the winter holidays. He listens to his family having a bitter argument about Parnell and the Catholic Church. When he returns to school, he finds out to his bewilderment that two of his classmates were caught doing something sexual with upperclassmen. A boy had broken his glasses, and a teacher beats him unjustly during one of his classes for sitting out. Stephen complains to the rector, who takes Stephen's side, and Stephen is cheered by his schoolmates.
We rejoin Stephen some years later. He spends a summer in Blackrock, exploring the neighborhood with his friend Aubrey, reading The Count of Monte Christo, and restlessly wandering the streets. Soon, due to financial troubles, Stephen's family moves to Dublin, where Stephen becomes infatuated with a girl named Emma Clery. They take the tram home together after a birthday party, and Stephen writes her a love poem.
The book leaps over a few years once again; now, Stephen is a high-achieving student at Belvedere, where he is known for his seriousness and studiousness. He has been getting into a bit of trouble with teachers and friends for his faintly heretical essays. He quibbles with his friends and plays the role of a pedantic teacher in a school play. Some time later, Stephen takes a melancholy trip to his father's hometown of Cork, during which he worries about his sexual longings, his cold indifference to others, and the end of his innocence. At the end of the year he is awarded a large sum of money for excellent academic performance, which brings him brief contentment. After he spends the money on friends and family, he becomes restless and unhappy once again. He becomes more and more sexually frustrated; despite great fear and shame, he begins to have sex with prostitutes.
Stephen’s class participates in a three-day religious retreat, composed mainly of fire-and-brimstone lectures about sin, hell, and suffering. The vivid lectures render Stephen’s guilt unbearable, and he decides to confess his sins and live purely and piously from now on. Soon, though, Stephen’s resolve begins to weaken, and he is beset by doubts. Just then, the director of Belvedere tells Stephen in a private meeting that he might be well-suited for the priesthood. The director’s flattering suggestion forces Stephen to make a decision: Stephen realizes suddenly that he finds a priest’s life repulsive and boring, and turns joyfully away from the religious life. Instead, he applies for admission to the University of Dublin. One day, as he walks on the shore, he realizes that his true calling is that of a writer; he looks at a lovely girl standing in the water and feels overcome with joy.
In the next scene, Stephen is a confident, well-respected student at the university. He skips many of his classes and spends most of his time walking around with his friends and holding forth about aesthetics. Only his friend Cranly can out-talk him, and only Cranly seems immune to the musty charm of Stephen’s strident theories. Stephen writes another poem for Emma, who still consumes his thoughts. In the book’s final pages, which take the form of diary entries, Stephen writes joyfully about leaving Ireland to find his destiny as a writer.