The twyning
by Terence Blacker
"This is a story of courage, of sacrifice, and of survival. This is the story of a rat and a boy whose fates become inextricably linked as their two worlds collide. Eften, a bold young ratling, dares to journey above the underground rat kingdom, where he discovers Dr. Ross-Gibbon's plan to exterminate the rat population. Dogboy, assistant to Dr. Ross-Gibbon, is an abandoned thirteen-year-old with a gift for understanding animals. As war wages between the human world and the rat kingdom. Doyboy must decide where his allegiances truly lie."