Servants Sam and Willie are practicing ballroom steps in preparation for a major competition, while maintaining Hally's mother's tea shop on a rainy day. Sam is the more worldly of the two. When Willie says his ballroom partner and girlfriend is lacking enthusiasm, Sam points out that Willie beats her every time she makes a mistake.
Seventeen-year-old Hally arrives home from school, and cheerfully asks about the dancing progress. Sam mentors the boy, wishing to guide him through adolescence into manhood, while Willie is the "loyal black"; who calls the white Afrikaner boy "Master Harold".
The conversation between the three moves from Hally's school-work, to an intellectual discussion on "A Man of Magnitude", where they mention various historical figures of the time and their contribution to society, to flashbacks of Hally, Sam and Willie when they lived in a boarding house. Hally warmly remembers the simple act of flying a kite Sam had made for him out of junk. Hally wishes to write a story about that kite for school, but he feels the ending was too simple, as he recalls how he had sat on a park bench to watch the kite fly, while Sam quietly went back to work. Conversation then turns to Hally's 500-word English composition, where they describe the ballroom dancing floor as "a world without collisions"; a transcendent metaphor for life.
Almost immediately, despair returns: Sam had early on mentioned why Hally's mother is not present; the hospital had called about his father, who has been there receiving treatment for complications from a leg he lost in World War I, to discharge him, and she had left to bring him home. However, Hally, indicating that his father had been in considerable pain the previous day, insisted that his father wasn't well enough to be discharged, and that the call must've been about a bad turn, rather than a discharge notice. A call from Hally's mother at the hospital confirms that Hally's father is manipulating the hospital into discharging him, although he is indeed not feeling any better than before, so it's still unofficial, and Hally remains hopeful that the discharge won't happen. A second call from Hally's mother later reveals that the discharge is official, and Hally's father is now home.
Hally is distraught about this news, since his father, who in addition to being crippled, is revealed to be a tyrannical alcoholic, and his being home will make home life unbearable with his drinking, fighting, and need for constant treatment, which includes demeaning tasks of having to massage his stump, and empty chamber pots of urine. Hally vents to his two black friends years of anger and pain, viciously mocking his father and his condition. But when Sam chastises him for doing so, Hally, although ashamed of himself, turns on him, unleashing vicarious racism that he learned from his father, creating possibly permanent rifts in his relationship with both Sam and Willie. For the first time, apart from hints throughout the play, Hally begins explicitly to treat Sam and Willie as subservient help rather than as friends or playmates, insisting that Sam call him "Master Harold" and spitting on him, among other things. Sam is hurt and angry about this, and both he and Willie stop just short of attacking Hally, but they both come to understand that Hally is really causing himself the most pain.
There is a glimmer of hope for reconciliation at the end, when Sam addresses Hally by his nickname again and asks to start over the next day, and maybe fly another kite, harkening back to the simple days of the other kite. Sam recalls the reason he had made that kite in the first place: Once, Hally's father had passed out from drunkenness at a hotel bar, and young Hally and Sam had to fetch him, as Hally's mother was unavailable to do so. Sam had to literally carry Hally's unconscious father home on his back, while young Hally miserably followed, carrying his crutches. Sam took pity on young Hally's shame and humiliation, and wanted to give Hally something to be proud of. In the present, Hally, horrified about what he's done, is barely able to face Sam, responds without looking up "It's still raining, Sam. You can't fly kites on rainy days, remember," and asks Willie to lock up the tea shop. Sam then gives Hally a twist ending to the kite story: the reason Sam left was because the bench Hally had sat on to watch the kite, had said "Whites Only" but young Hally had been too excited to notice it, but now, he can (figuratively) leave it at any time. Hally exits into the rain without response. The play ends while Sam and Willie consoling each other by using Willie's bus fare to play the jukebox, and they ballroom dance together.
