The Swords of Lankhmar
Fritz Leiber
 The Fafhrd and Gray Mouser stories follow the lives of two larcenous but likable rogues as they adventure across the fantasy world of Nehwon. In The Swords of Lankhmar the duo is hired by the city of Lankhmar to protect its grain fleets, which have fallen prey to a mysterious threat. A sea serpent ridden by an explorer from another world is encountered, but the true foes prove to be legions of intelligent rats. Returning to Lankhmar, the protagonists find the whole city under siege by the rats. The Mouser, magically shrunken to rat size, spies out their plans, but the rats' victory appears certain until the intervention of the Gods of Lankhmar and the rats' own ancient enemies.