Seventeen-year-old Hally spends time with two middle-aged African servants, Sam and Willie, whom he has known all his life. On a rainy afternoon, Sam and Willie are practicing ballroom steps in preparation for a major competition. Sam is quickly characterized as being the more worldly of the two. When Willie, in broken English, describes his ballroom partner (his girlfriend) as lacking enthusiasm, Sam correctly diagnoses the problem: Willie beats her if she doesn't know the steps.
Hally then arrives from school. Sam is on an equal intellectual footing with Hally; Willie, for his part, always calls the white boy "Master Harold." The conversation moves from Hally's school-work, to an intellectual discussion on "A Man of Magnitude", 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; we later learn that Sam made it to cheer Hally up after he was embarrassed greatly by his father's drunkenness. Conversation then turns to Hally's 500-word English composition. The play reaches an emotional apex as the beauty of the ballroom dancing floor ("a world without collisions") is used as a transcendent metaphor for life.
Almost immediately despair returns: Hally's tyrannical father has been in the hospital because of medical complications due to the leg he lost in World War II, but it appears that today he is coming home. Hally is distraught about this news, since his father being home will make home life unbearable. He unleashes on his two black friends years of anger, pain and vicarious racism from his father, creating possibly permanent rifts in his relationship with them. 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 but understands 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, hearkening back to the simple days of the kite. Hally responds "It's still raining, Sam. You can't fly kites on rainy days, remember," then walks out into the rain. The play ends while Sam and Willie console each other by ballroom dancing together.