Although young Montague Mad-Rat lives inor rather, underNew York City, he know very few rats besides his mother, who makes hats, his father, who builds mud castles, and his globe-trotting Aunt Elizabeth. But Montague’s life takes an abrupt turn for the eventful the stormy day he meets Isabel Moberly-Rat on his way home from Central Park.

Home, for Montague, is an old sewer pipe. He now learns that there is a city full of other rats out there who inhabit abandoned piers and lead considerably less eccentric and more luxurious lives than his family. What is more, these rats are in the midst of a grave crises. A human being has decided to turn their piers into parking lots, and an extermination campaign is already under way.

As Montague stumbles into this wider, bewildering world, he longs to help ratdom (and impress Isabel). But how much can one rat really do, especially when he’s an outcast?