It all started when a certain magic item was accidentally dropped down a storm drain…
	Several rats and mice have been randomly "Awakened" at birth; they gained human-like intelligence and prehensile hands. It's semi-heritable - at birth, an Awakened mother can make an IT roll for each child to Awaken them.
	This has been going on for many generations, and now the stormsewer mains are plied by rodent merchant ships, ranging from 10 to 25 decimeters long. These also carry the rodent language, Stormtongue, and knit together a very loose society. Until recently, the merchant ships have been valued by all… But a ship rat named Crow changed all that.
	Crow discovered the house of a human mage; mages are rare among humans, and Crow moved to monopolize this resource and loot it for all it was worth. With some early items he bought a ship and a crew of goons, and for days he rudely dominated the western mains in order to ship his cargo without anyone else getting close.
	Such precious cargo in such unpleasant hands proved too tempting a target, and piracy came to the stormsewer mains with a vengeance. It quickly spilled over to raiding other ships, and even after Crow left for points unknown the damage had been done.