A deadly virus killed every adult on Earth, leaving only the kids behind. With her parents gone, Lisa is responsible for her little brother, Todd. She has to make sure they stay alive. Many kids are sick or starving, and fierce gangs are stealing and destroying everything they find. Lots of people have given up, but on Grand Avenue, some kids are surviving. Because of Lisa.
Lisa figured out how to give the kids on Grand Avenue food, homes, and protection against the gangs. But Tom Logan and his army are determined to take that away and rule the streets themselves. How long can Lisa's group keep fighting them off? They need to find a place to live safely. A strong place. A secret place.
In a world like this, someone has to take charge. But does Lisa have the strength to take charge of a whole city?
A plague turns everyone on Earth over the age of twelve to ash. In a suburb of Chicago, ten year old Lisa Nelson uses her intellect to thrive in a world without adults or utilities. With ingenuity, she manages to operate a car and scavenge from farm houses. After dropping off a haul at home, her younger brother Todd is attacked and robbed by the Chidester Avenue Gang. This prompts Lisa to organize the neighborhood kids in defense against roving thugs.
Lisa initially has success safeguarding the neighborhood and in locating a wholesale warehouse with her new friend Craig. However, after a standoff with Chidester's leader Tom Logan, the Nelsons are burned out of their house. Lisa realizes that the local high school is the safest shelter in the area, and works with her friends to fortify it in secret. Despite the work everyone does, Lisa insists that it is "her" city, since all the best ideas have been hers, and everything would break down into squabbles without her guidance. The viewpoint irks many of "her" citizens, but any unrest is quieted by her accomplished, effective leadership.
During an unsuccessful raid on the school, Tom Logan is disfigured with hot oil, which seems only to steel his resolve. Logan finally manages to trick Lisa into exiting the school, after which she is shot and left for dead. Todd, Craig and de facto nurse Jill rescue Lisa and tend to her at a farmhouse. Craig wants to give up on the school, and when Lisa refuses, quits the group. Todd returns to the school as a spy, and learns that Tom Logan has alienated most everyone there with a reign of terror that fails to sustain the community.
Lisa and company travel to nearby towns in search of mercenaries to help retake the school. They prove unnecessary, as there is a mass exodus from the school as soon as word gets out that Lisa is still alive. Lisa sneaks in alone to confront Tom Logan, who ultimately recognizes his failings and voluntarily leaves with his gang. The kids return to the school, chanting Lisa's name.