Hopper is just an ordinary pet shop mouse before he escapes. Soon he finds himself below the bustling streets of Brooklyn, deep within the transit tunnels, and in Atlantia, a glorious utopian rat civilization. Soon, Hopper is caught in the crosshairs of a colossal battle, one that crosses generations and species. As the clashes rage, Hopper learns terrible, extraordinary secrets. Deadly secrets about Atlantia. Painful secrets about his friends. And one powerful secret about his destiny.