Winnie's last day of fourth grade ended with a pretty life-changing surprise. That was the day Winnie's parents got divorced, the day they decided that Winnie would live three days a week with each of them and spend Wednesdays by herself in a treehouse smack between their houses, to divide her time perfectly evenly between them. It was the day Winnie's seed of frustration with her parents was planted, a seed that grew and grew until it felt like it was as big as a tree itself. By the end of fifth grade, Winnie decides that the only way to change things is to barricade herself in her treehouse until her parents come to their senses, and her friends decide to join her.