Mrs V recommends... Warriors - Into the Wild by Erin Hunter
For generations, four Clans of wild cats have shared the forest according to laws laid down by their ancestors. But the ThunderClan cats are in grave danger as the sinister ShadowClan grows stronger every day. In the midst of this turmoil appears a house cat called Rusty, who may turn out to be the bravest warrior of all.
I've chosen this book, which is the first in a number of series and spin-offs, because my daughter really enjoyed reading them through her junior school years. There's even a website! You can do an online quiz to find out which Clan you would be in if you were a cat... I would be in WindClan! :)