Montague Mad-Rat lives a solitary existence in the sewers of New York City. His only delights are scavenging through Central Park for feathers and berries for his mother, and painting the seashells his aunt brings him. One day, he rescues the beautiful Isabel Moberly-Rat, and upon escorting her home is introduced to a world he never knew existed. For she lives at the wharves, in a spacious crate, among rats who look down on those like him who make things with their paws. Suddenly Montague is ashamed. So when he hears about the campaign to save the wharf from human destruction, he does all he can to help. But how much can one rat really do, especially when hes an outcast?