The Ghost in the Trees - Gnaverworld: Ghosts and Iron, #1

Rodents rule and trees pierce the clouds in Gnaverworld. Risu is the Ghost-trained in the art of stealth and sabotage. After her village is attacked, Risu sneaks away to the big city to deliver a message to their allies. But when she comes home, she finds her village aflame and her family disappeared. Her adopted brother and sword-wielding rival agree to help her find her family at the evil emperor's citadel in the capital.
The fastest route is through the dark Sea of Trees, where they have to navigate wild animals and roaming bandits. Fans of REDWALL and USAGI YOJIMBO will love the high-flying, blade-slicing action of THE GHOST IN THE TREES.