Josephine, who goes by Fin, writes about her experience at Camp Moonflower in a notebook which she hides in her trunk under her sanitary napkins. The summer camp that Fin attends is for young girls who have started to menstruate to learn how to be a proper woman and a future wife. They do activities like perfecting apple cheeks and swimming, and wear all white. Fin was told to address the letters in her diary to her future husband, and she does so for the first few days, but after Captain Bev, whom the girls call Beaver, tells Fin she that she has written the letters all wrong, Fin transfers them to her notebook and hides it. Fin is a girl with big breasts, too big for her small body, and she bunks with Pita, short for Pain in the Ass, a stick-like girl who tries her hardest to be promiscuous. Pita talks about porn and teaches the other girls swear words. Pita even brings a dildo to camp. Pita develops a crush on one of the male counselors, Andrew, and tells her very sexual fantasies to the other girls in the cabin. The girls participate in a variety of strange activities, such as the Black Night Ceremony, where ghost stories are told and the male counselors wear sacks over their heads. Fin is even inducted to the Sisterhood, a special privilege that some of the girls are granted, including Fin's flute-playing cabin-mate Caroline. Fin prefers horse-riding, and she decides that she likes a horse called Jo, even though she is fat and does not gallop. Andrew comes over to Fin while she is riding Jo; he touches her thigh and tells her that he will teach her how to ride a real horse after taps the next day. Fin gets ready to see Andrew and hides the secret meeting. Andrew gets on a horse with her, and the two ride until Fin's butt hurts. The next day, someone poorly forges a note in Fin's handwriting saying that she wants Andrew to touch her boobs. Fin realizes that Pita has written the note but does not defend herself. Fin is given a talking to by the Beaver and thinks she will be asked to leave camp; instead, the next day, she is put in a canoe and rowed out to shore by a male counselor with a sack over his head. Fin starts screaming. Eventually, the counselor stops the canoe and tells Fin that she has been picked to represent Womanhood through the ultimate Test of Steadfastness: jumping into the lake and swimming back to camp. Fin can only dog-paddle, but she knows the way back and jumps into the water.