It is the middle of the night, and Megan Nowicki hopes she left her glasses in her treehouse fort. She goes out to the fort and finds them there. Before returning inside, she hears an unexpected crash from her neighbor’s yard. Looking through her binoculars, she sees monkeys climbing on the roofs—monkeys that escaped from the nearby zoo. She fetches her brother, Noah, to show him, but the monkeys are gone and he doesn’t believe her. Back inside, Megan writes a three-page journal entry about the evening’s events.

Two months later, 14 frogs in the zoo’s Creepy Critters exhibit find the pages from Megan’s journal; they are looking for a girl who broke into the zoo a few minutes earlier.

Several months later, Megan Nowicki is missing. The town spent a month looking for her before everyone gave up except her brother, Noah, and their friends, Ella and Richie. They continue to ask questions and investigate her disappearance. The four friends call themselves the “Adventure Scouts.” Noah climbs to their treehouse, Fort Scout, to raise the red distress flag, hoping Ella or Richie will see it and come running. While he waits, he remembers the night Megan told him she saw escaped monkeys running on the rooftops; Noah didn’t believe her, but now he wonders if the zoo and her disappearance are connected.