Tom Moorhouse 
Trickster [EPUB ebook] 

First a rat must earn his name. Then he must live up to it. This is the story of Gabble, a young rat with a wild, beloved, but unpredictable brother, Ash. At the start of the book Ash tricks Gabble into going out with him on a 'name raid’, a dangerous mission to earn a True Name, normally reserved for older rats. Gabble finds himself drawn into a perilous adventure, crossing boundaries, fighting with enemy rat packs, and eventually being forced to confront both his brother and himself in the most dramatic fashion.