Among the Hidden is a thought-provoking story set in of the not too distant future that explores the choices and challenges faced by an early adolescent boy as he struggles to find his place in a world in which his existence is illegal. Luke, a third child, lives in a future where each family is allowed to have only two children. Because his parents broke the population laws when they let him live, Luke must stay hidden in his house, has never been to school, must eat in the attic stairwell to avoid being seen, and must spend his days with nothing to do except re-read a few old books and observe his neighborhood through the attic air vents.

When he discovers another third child, Jennifer Rose Talbot, also hiding in his neighborhood, he dares to venture outside his attic-hiding place and thus discovers a network of hidden children who communicate via Internet chat rooms. As Luke's friendship with Jen grows, he learns that she is organizing the hidden children to protest against the government's oppressive laws, and he must decide whether to defy the government and seek freedom. In this futuristic dystopia, Haddix explores the consequences of population control and other policies of a totalitarian government on individuals living in that society, and she explores how far an individual will go to have a life that is worth living.