On the Fourth of July, Sister’s uneventful life in China Grove is interrupted by the arrival of her sister, Stella-Rondo, who has just left her husband, Mr. Whitaker, and returned to the family home in Mississippi. Sister had briefly dated Mr. Whitaker before Stella-Rondo became engaged to him. Stella-Rondo arrives from Illinois, accompanied by Shirley-T., a little girl she claims is her legally adopted daughter. The rest of the family, overjoyed at Stella-Rondo’s return, does not share Sister’s suspicion that Shirley-T. is actually Stella-Rondo’s biological daughter. When Sister questions Shirley-T.’s dubious parentage, Stella-Rondo angrily orders Sister to never mention the matter again. In an attempt to turn Papa-Daddy against Sister, Stella-Rondo claims that Sister suggested that Papa-Daddy should trim his long, grizzled beard. Papa-Daddy believes Stella-Rondo’s false claims and angrily reminds Sister that he was the one who secured her the job as the town’s postmistress. Sister promptly leaves the table, while Papa-Daddy skulks outside to lie in the hammock. Uncle Rondo soon appears in the hall, dressed in Stella-Rondo’s kimono. Woozy from excessive doses of a prescription medication, he heads to the yard, where Papa-Daddy relays what he believes the ungrateful Sister has said about his beard.
Sister then hears Stella-Rondo open one of the upstairs windows and goes to join her. Stella-Rondo asks Sister to look out into the yard and tell her what she sees, upset and embarrassed that Uncle Rondo has taken the kimono in which Mr. Whitaker had once photographed her. Sister defends Uncle Rondo and chastises Stella-Rondo for being overly critical, especially after suddenly appearing with an adopted daughter and imminent divorce. Stella-Rondo reminds Sister that she vowed never to speak of Shirley-T. again. Miffed, Sister goes to the kitchen to make green-tomato pickles, as the servants had been given the day off for the holiday.
Mama comes in and expresses her disapproval at Sister making a food that will not agree with Uncle Rondo and Shirley-T. Sister points out that she would have been given a much different reception if she had been the one to return home from Illinois under such questionable circumstances. Mama reminds Sister that she was spurned by Mr. Whitaker and that if she had been the one returning home, her welcome would have been no less warm. Sister disagrees and attempts to convince her mother that Shirley-T. is not adopted. Mama refuses to recognize the truth. Sister then wonders out loud whether Shirley-T. is even able to talk, and she hints that the child might have a developmental disability. Mama shouts up the stairs to relay Sister’s concerns. Angered at the accusation, Stella-Rondo has Shirley-T. sing the theme song to Popeye the Sailor Man, a performance that is followed by the child tap-dancing loudly. Satisfied, Mama insists that Sister apologize for her accusation, but Sister refuses. Mama furiously stalks upstairs to embrace her adopted granddaughter.
Next, Stella-Rondo sees to it that Uncle Rondo, too, turns against Sister. Stella-Rondo claims that Sister has been sneering at Uncle Rondo’s ridiculous appearance. Angered, Uncle Rondo strips off the kimono, throws it on the ground, and stomps on it, grinding it into the dirty floor. His anger continues to simmer that night, as he plays cards with Mama and Stella-Rondo. Then, unexpectedly, at 6:30 the next morning, he throws an entire package of lit firecrackers onto the floor of Sister’s bedroom. The ensuing racket unsettles Sister’s already delicate nervous condition. Sister immediately decides that it is time for her to move to the post office. Making her intentions obvious, she goes through the house collecting her belongings, including a prized possession—a radio. Mama objects to the removal of a pair of vases. Sister fires back that if Mama wishes to see them, she can always come down to the post office. The family then uniformly asserts that they will never set foot in the post office or send or receive mail.
Sister responds that, without the post office, Stella-Rondo won’t be able to be in touch with Mr. Whitaker. This possibility prompts a flood of tears from Stella-Rondo. Mama expresses dismay that the joyous return of Stella-Rondo on a major holiday could turn so sour. Sister declares that it was Mr. Whitaker who left Stella-Rondo, not the other way around, and that she, Sister, had predicted exactly how things would turn out. Still crying, Stella-Rondo shuts herself in her bedroom. Sister hires a girl with a cart to haul her belongings to the post office.
Five days later, Sister has yet to hear from her family, but she convinces herself that she is happy to be alone. There is little mail to attend to, and the people in town are divided in their support of her actions. Sister asserts that if Stella-Rondo appeared at the post office and was forthcoming about the details of her life with Mr. Whitaker, Sister would plug both of her ears with her fingers and refuse to listen.