Stephen, now a teenager, is a student at Belvedere College, a Jesuit school. He is preparing for a performance in the play the school is putting on for Whitsuntide, the Christian feast of Pentecost. Stephen is to play the role of a farcical teacher, a role he has won because of his height and his serious manners. After watching various others get ready for the performance, he wanders outdoors, where his school friend Heron and Heron's friend Wallis greet him. Heron encourages Stephen to imitate the school rector when performing the role of the stodgy teacher. The two boys tease Stephen for not smoking. Wallis and Heron also playfully mention that they saw Mr. Dedalus arrive at the theater with a young girl. Stephen imagines that the girl is the one Stephen had flirted with earlier at the birthday party. Wallis and Heron playfully try to force Stephen to confess his dalliance with the girl.
Stephen suddenly recalls a dispute with Heron and two other students over the question of which English poet is the best. Stephen had named Byron, while the other student had said that Tennyson was obviously superior. Remembering this quarrel, Stephen reflects on his father's command for him to be a good gentleman and a good Catholic, but the words sound hollow in Stephen's ears now. Stephen is shaken from his reverie by a reminder that the curtain will go up soon. Stephen performs his role successfully. After the play, he does not stop to talk to his father, but goes walking in the town, highly agitated.
Stephen and his father sit in a railway carriage bound for the city of Cork, where his father is auctioning off some property. Stephen is bored by his father's sentimental tales of old friends and annoyed by his drinking. Falling asleep at Maryborough, Stephen is awakened by a frightening vision, in which he imagines the villagers asleep in the towns passing by outside his window. After praying, he falls asleep again to the sound of the train.
Stephen and Mr. Dedalus take a room at the Victoria Hotel. Stephen lies in bed while his father washes and grooms, softly singing a tune from a popular variety show. Stephen compliments his father on his singing. At breakfast, Stephen listens while his father questions the waiter about old acquaintances, and the waiter misunderstands which men Mr. Dedalus is discussing.
Visiting Mr. Dedalus's medical school, Stephen comes upon the startling word "Foetus" carved into the top of one of the desks in a lecture hall. Stephen has a vision of a mustached student carving the word years ago, to the amusement of onlookers. Leaving the college, Stephen listens to his father's stories of the old days. Mr. Dedalus tells Stephen that he should always socialize with gentlemen. Stephen feels overwhelmed by a sense of shame and alienation, and regains his grip on himself by telling himself his own name and identity. Going from bar to bar with Mr. Dedalus, Stephen is ashamed by his father's drinking and flirtation with the barmaids. They encounter an old friend of Mr. Dedalus, a little old man who jokingly claims to be twenty-seven years old. Stephen feels distant from his father, and recalls a poem by Shelley about the moon wandering the sky in solitude.
Stephen grows increasingly alienated from his father, largely because of Mr. Dedalus's inability to connect with reality. Stephen is bored by his father's tales of the old days as he rides with him in the train to Cork. He sees how much his father has lost touch with the world: Mr. Dedalus is unable even to talk to the hotel waiter about common acquaintances, as he and the waiter get mixed up about which acquaintance they are discussing. Mr. Dedalus's failure to keep up with the times seems pathetic, and we sense that his constant drinking throughout this nostalgic trip home is an attempt to protect himself from the pain he cannot face directly. Mr. Dedalus revisits his former medical school, perhaps to recapture his lost youth, but the visit is repulsive to Stephen, who has a vision of a student from his father's era carving the disgustingly incongruous word he sees on the table. Here again, Mr. Dedalus's blithely sweet memories of the past seem irrelevant to the family's hard times in the present, and his drunken denial of the reality around him alienates his son. When Stephen states his name for his own reassurance, saying, "I am Stephen Dedalus," we sense that he feels the need to assert his own identity because his father's identity is rapidly crumbling.
Stephen's role in the Whitsuntide play foreshadows the role of hero he later aspires to fulfill. The fact that Stephen has been chosen to play a teacher is significant, but also ironic, as the role requires that Stephen play the teacher comically rather than seriously. This parody of a teacher figure hints at the novel's underlying doubt about the validity of leading or instructing others. Stephen performs the role successfully, and is amazed at how lifelike the play feels: the "disjointed lifeless thing had suddenly assumed a life of its own. It seemed now to play itself. . . ." The life Stephen discerns in the play makes him aware of the importance of acting as a metaphor for living. Stephen's awareness of life's drama becomes problematic, however, when the things he previously thinks real begin to appear false. He reflects on the moralizing voices of his early years that "had now come to be hollow-sounding in his ears." Art and life are, in a sense, switching places: while the artistic performance seems lifelike, life itself seems artificial.
Joyce's experimentation with the technique of stream of consciousness—capturing the processes and rhythms by which characters think—is especially evident in the sudden flashbacks of the play scene. Joyce narrates Heron's and Wallis's near violent teasing about Stephen's flirtation with the girl in the audience. Then suddenly, without any warning, Joyce takes us back to Stephen's first year at Belvedere, when he was accused of heresy because of a mistake he made in an essay. This memory segues into another memory from a few nights after the first, when Stephen was forced into a ridiculous schoolboy argument about the relative merits of Byron and Tennyson. When this argument is finished, the narration returns to the scene of the play in the present moment. Joyce wants us to feel unsettled and even a bit confused by these unannounced leaps from present to past. The time shifts represent the way Stephen's mind—and the human mind in general—impulsively makes constant connections between experiences from the present and memories from the past. We are never told why Stephen's mind links the girl, the literary dispute, and the heresy accusation, which leaves us with an impression of psychological complexity that we cannot fully unravel.