Into the Wild - Erin Hunterová

For generations, four Clans of wild cats have shared the forest according to the laws laid down by their ancestors. But the warrior code has been threatened, and the ThunderClan cats are in grave danger. The sinister ShadowClan grows stronger every day. Noble warriors are dying--and some deaths are more mysterious than others. In the midst of this turmoil appears an ordinary housecat named Rusty... who may turn out to be the bravest warrior of them all.