Hopper is just an ordinary pet-shop mouse before he escapes. Soon he finds himself below the bustling streets of Brooklyn, deep within the untamed tangles of transit tunnels, and in Atlantia, a glorious utopian rat civilization. But all is not what it seems. Though Hopper is treated as a royal guest, he misses the siblings he lost in the escape attempt. And not only is Atlantia constantly threatened by the rebels who wish to bring the city to its knees, there are cats everywhere; cats that leave the citizens unharmed, and no one can seem to answer why. Soon, Hopper is caught in the crosshairs of a colossal battle that involves different generations and species. As the clashes rage, Hopper learns terrible, extraordinary secrets: Deadly secrets about Atlantia. Painful secrets about his friends. And a powerful secret about his destiny.