Set in Belfast in 1908, the story follows Davy Caruth, a 12-year-old working-class boy whose family struggles to make ends meet. His father, Sam (Da), can no longer work at the local shipyard due to a bad back and now drives a bread cart for a demanding boss named Billy Givens. His mother, Sarah (Ma), works as a housemaid for the Lewis family at their large house, Little Lea. One spring morning, Ma brings Davy along, hoping he can earn extra money doing chores.
At Little Lea, Mrs Lewis surprises them by suggesting Davy play with her younger son, Jacks, who is nearly 10 and lonely since his older brother Warnie left for boarding school in England. The cook, Mrs Conlon, mentions that Mrs Lewis recently had an operation to remove a lump. Ma is disappointed that Davy will not be working but agrees. Jacks is shy and clumsy at football, but in the attic playroom he comes alive, showing Davy the view of Cavehill, a hill whose profile resembles a sleeping giant, and lending him
Gulliver's Travels. Jacks and Warnie write stories and draw maps of an imaginary land called Boxen, and Jacks tells Davy that making things up is "a very mysterious thing" (39). Davy is intrigued but bewildered.
At home, Davy reads the book aloud to his six-year-old sister, Minnie, but Ma catches him and scolds him for borrowing from the Lewis household. She insists books are "not for people like us" (33) and orders the book returned on Monday. Defiantly, Davy stays up late Saturday night to keep reading. After a nightmare about the workhouse, the dreaded institution for the destitute, he finishes the book by candlelight. Ma tells Davy plainly that Da barely earns enough and orders him to focus on working, not playing.
Despite Ma's warnings, the friendship deepens. Jacks offers more books, which Davy reads at the Lewis house to avoid trouble at home. When Jacks asks him to sketch a squirrel character for a story, Davy discovers a talent for drawing. The sketch is so good that Jacks pins it on the wall and tells Davy he could be an artist, planting a seed of ambition. The boys venture into Belfast together, playing make-believe at Jacks's grandmother's house and watching a
Gulliver's Travels film at the Empire Palace of Varieties. When the doorman at Robinson & Cleaver's department store snubs Davy, Jacks pointedly names him on the way out, insisting on equal treatment. That evening, Davy gives Minnie a saved chocolate bar and promises to take her to the Empire someday.
Ma warns Davy that their world will never be like the Lewises'. Mrs Lewis advocates for the friendship, and Davy negotiates a compromise: chores in the morning, time with Jacks afterward. For Davy's birthday, Mrs Lewis takes both boys to the Giant's Causeway on the Antrim coast, where Davy tells Jacks the legend of Finn MacCool, the mythical Irish giant, and realizes his father's old tales have value. In a forest, they pass under an archway that Jacks calls the home of a magician and enchantress, and Davy is swept up in the make-believe. On the train home, Mrs Lewis, with tears in her eyes, tells Davy to cherish his own mother, hinting at her worsening illness.
Mr Lewis offers to use his family's influence to get Davy a position at the McIlwaine and Lewis shipyard. Davy accepts, but the reality is grim: The foreman, Murphy, shows him rivet teams where boys hold red-hot metal in tongs and throw it to a catch-boy dangling from scaffolding on the ship's hull. Boys are regularly maimed or killed. Davy is assigned as heater boy and told to lie about his age. That night, he breaks down to Da, who comforts him and promises to pray for something better.
When Davy visits Jacks on a Sunday, he collides with a nurse carrying a basin on the landing, realizing someone is seriously ill. Jacks admits his mother's condition has worsened and breaks down, saying she gave him a Bible and he does not want it; he just wants his mother. Davy confesses he hates the shipyard, and the two comfort each other. Da takes the boys to a road bowling match, a traditional Irish sport played along country lanes. Some men harass Jacks for being upper class, but Da defends the boys. When they return Jacks home that evening, Mr Lewis comes out looking grim and leads Jacks inside. Ma reveals that Mrs Lewis has taken a severe turn, and Warnie has been sent for from England.
A few weeks later, Mrs Lewis dies. Davy sneaks out to the Lewis house during the wake, where Jacks tells him he is leaving for school in England with Warnie right after the funeral. Davy visits on the remaining Sundays, but when he goes to buy a farewell gift, Ma tells him Jacks has already left without saying goodbye. Davy runs to the Lewis house and finds it dark and empty.
Da convinces Ma to let Davy attend Technical Drawing classes at the Blackman Technical College in the evenings. Davy's teacher praises his work and suggests he might qualify for hours in the drawing office at the larger shipyard. Then Davy receives a letter from Jacks describing a brutal school with a headmaster who beats boys severely. Ma refuses to intervene with Mr Lewis, so Davy visits Mr Lewis himself. Mr Lewis is initially dismissive but grows thoughtful, admitting the house is terribly quiet without his wife. He promises to look into the matter. Davy writes back to Jacks, enclosing a drawing of a red squirrel with a bow tie.
The following spring, a catch-boy named Bobby Thompson falls from the scaffolding and is killed. Davy resolves never to return, but he arrives home to find that Givens has sacked Da from the bread cart. Davy confronts Givens, who refuses to relent and threatens to have Davy sacked too. With Da now unemployed, Davy has no choice but to keep going back to the dangerous yard.
Over a year later, in autumn 1910, Mr Chisholm, the chief draughtsman, offers Davy a full-time apprenticeship in the drawing office. Davy accepts, overjoyed to leave the rivet team. That evening, he presents Ma with his larger pay envelope, and she embraces him proudly. Overhearing his parents afterward, Davy hears Ma concede that filling children's heads with stories is not such a bad thing. Ma tells Davy that Jacks also has good news.
Davy runs toward the Lewis house but collides with Jacks on the road. Jacks has been looking for Davy's house; he weeps, saying he still misses his mother. Jacks reveals that Mr Lewis has enrolled him at Campbell College, a boarding school in Belfast, instead of sending him back to England. On Saturday, Davy visits Jacks at Campbell and gives him a framed drawing of Cavehill with the sleeping giant, the same view from the attic where their friendship began. As Davy leaves, he pauses on the wooded drive, reflecting on how Jacks changed his life: Without Jacks, he would never have pursued drawing or earned the apprenticeship. A squirrel darts out of the trees, stops, looks at Davy, and bounds away. Davy laughs, puts his hands in his pockets, and walks home.