When a widower receives the devastating news that he doesn't have long to live, he is struck by the question of who will care for his adult son - a son whom he fiercely loves, a boy with Down syndrome. With no recourse in mind, and with a desire to see the country on one last trip, the man signs up as a census taker for a mysterious governmental bureau and leaves town with his son. Traveling north, farther into the country, through a tapestry of towns napes only by ascending letters of the alphabet, the man and his son encounter a wide range of human experience. While some townspeople welcome the pair into their homes, others, who bear the physical brand of past censuses on their ribs, are wary of their presence. Toward the edges of civilization, the landscape grows wilder and the towns grow farther apart and more blighted by industrial decay. As they approach Z, the man must confront a series of questions: What is the purpose of the census? Is he complicit in its mission? And just how will he learn to say goodbye to his son?