Frankie Addams is a 12 year old who describes herself as detached. That would make sense, given that her mother died during Frankie's delivery over a decade ago. Her father is also aloof, leaving Frankie in the company of Berenice Brown, their maid. She also gets to hang out with John Henry West, her 6 year old cousin. She has an older brother, Jarvis, who is engaged to be married to Janice Evans.
On the last Friday in August, young Frankie discusses marriage with Berenice and John Henry, basically saying that she doesn't really understand the point. Berenice says that it's probably just a little jealousy and sends them to bed. Sometimes Frankie sleeps next to John Henry, because she gets lonely. She used to sleep with her father, but then one day, he told her she'd gotten to be too old for that. Also, the family has the war to think about, WWII, that is. Frankie is on the cusp of sexuality, but doesn't pursue it for now. Instead she spends her next day, Saturday, thinking of her life and ultimately concluding that she feels jealous of Jarvis and Janice because she is part of the same thing that they are—they're one family.
Frankie decides in the afternoon that she'll be called F. Jasmine, to fit in with Jarvis and Janice better. She goes on a walk through the town and explains to the townspeople that she plans to runaway with the newlyweds. Her father treats her just the same though when she reaches him at the jewelry shop where he works. He tells her that Uncle Charles has died. She tries to be mature about it. Then, she goes into a bar and invites a soldier on a date, another attempt to be mature.
At dinner, Berenice and John Henry join Frankie for a conversation about love and marriage. They each try to explain how they would do these things differently if they were God. "F. Jasmine" explains that if she were God, boys and girls could switch genders at will. They continue talking until they suddenly realize that they accidentally arrived at an interesting commentary of racism—Berenice is black, after all.
F. Jasmine goes to a psychic for a fortune telling. The psychic tells her she will fail to sneak away with the newly weds. She goes to her date with the soldier who tricks the young preteen into coming with him to her hotel room. When he tries to engage her sexually, she bashes him across the head with a pitcher and runs away.
At the wedding, she is called "Frances." As predicted, she tries to talk to Jarvis and Janice, but they reject her efforts, so she takes her father's handgun and runs away. But the police bring her home. In the end, Berenice decides to quit her job as their maid, and John Henry unfortunately dies. Frances makes a friend named Mary, but it looks like she and her father will be moving soon.