When a mysterious virus kills everyone over the age of twelve, ten-year-old Lisa Nelson and her younger brother Todd are left to survive in a chaotic, empty world. Seeing the danger from roaming gangs, Lisa has a bold idea: she and the neighborhood kids must claim and defend an entire abandoned high school, turning it into their fortress and new home—Grand Avenue School. As the self-proclaimed 'owner' of this city, Lisa must use her intelligence, courage, and leadership to solve problems of food, safety, and community, facing off against a menacing gang leader who wants to take everything she's built.