One day in class, Mr. Birkway reads Longfellow's "The Tide Rises, the Tide Falls," which tells the story of a man traveling at night by the sea who mysteriously disappears. The students discuss their interpretations of the poem: Sal, for one, is sure the man died, and Phoebe follows her lead, arguing that the man was murdered. When Ben suggests that the man died normally, Sal retorts that death is never normal. Ben responds by suggesting that terrible things can be normal as well. Upset by the poem, Sal and Phoebe race to the police station after school. Phoebe shows the skeptical Sergeant Bickle the evidence she has collected. Mr. Bickle calls Mr. Winterbottom, who takes the girls home. Phoebe insists to Mr. Winterbottom that Mrs. Winterbottom is the victim of foul play, explaining that Mrs. Winterbottom loves Phoebe too much to leave her without any explanation. At this, to the girls' shock, Mr. Winterbottom begins to cry.
One night, after Mrs. Cadaver has left to work the late shift, Phoebe and Sal sneak into Mrs. Cadaver's darkened house. Inside, they find Mrs. Partridge, reading in the dark. When they turn on the lights, the girls are taken aback by the room's unusual furnishings. Phoebe observes the room intently, cataloguing suspicious items. As the girls are leaving, Mrs. Partridge tells them that she has met Phoebe's brother, but Phoebe, perplexed, insists that she does not have a brother.
On their way home, Sal, remembering her own mother, tries to tell Phoebe that Mrs. Winterbottom may have wanted to leave, but had not been able to explain why she wanted to leave to Phoebe. She goes so far as to suggest that Mrs. Winterbottom might not come back, and Phoebe silences her vehemently. Sal lays awake that night, thinking of how she used gifts and objects to remember her mother after she was gone, and musing on the Longfellow poem and Mr. Winterbottom's tears.
The next day, another note, bearing the message, "We never know the worth of water until the well runs dry" appears on Phoebe's doorstep. Before school, Sal and Ben are talking at Ben's locker, and Sal almost kisses him, but misses him and ends up kissing the locker. In English class that day, the students discover, much to their horror, that Mr. Birkway intends to read excerpts from everyone's journals to the rest of the class. He changes the names used in the journals and hides their covers, but everyone can tell who is writing and about whom he or she is writing by the writer's language and topic. One by one, students burst out in anger at each other, as Mr. Birkway, enjoying the "honesty" or "conflictual emotions" of the passages, reads out from journal after journal.
After school, Phoebe and Sal run to the police station once again with the new message and the "clues" in Mrs. Cadaver's house. Sergeant Bickle leads Phoebe out of his office, and Sal idly glances over the pictures on his desk. To her shock, she sees a photo of Sergeant Bickle, his wife, and the lunatic.
Sal and her grandparents reach Yellowstone National Park in the evening and find a motel, planning to see Old Faithful in the morning. Before they go to sleep, she continues Phoebe's story. On her way home from the police station, Sal walks past Mrs. Cadaver's house. To her surprise, Mr. Birkway appears, ready to escort Mrs. Partridge to an event. She soon learns that Mr. Birkway and Mrs. Cadaver are twins, and Mrs. Partridge is their mother. Sal tries to find Phoebe and tell her, but cannot find or contact her at all that night. The next day at school, Phoebe refuses to tell Sal where she was the night before. Sal's perplexity with Phoebe dissipates as Mr. Birkway resumes reading from journals. One writer expresses frustration with English class and its obsession with text and symbols, which causes Mr. Birkway to use an optical illusion to demonstrate how amazing it is to be able to see one thing in two—or more—ways. Then he reads from Sal's journal. The class titters at Sal's tree-kissing proclivities, but is quickly distracted from their amusement when Mr. Birkway, to his increasing chagrin, reads aloud Phoebe's journal entry, which contains her suspicions about Mrs. Cadaver. Chaos breaks out in the class as the bell rings.