The Outlaw Varjak Paw by S. F. Said
Having saved the city cats from a fate worse than death, Varjak Paw finds himself the leader of a new gang. But will the pressure take its toll on this brave but sometimes naive cat? Soon the city erupts in an all-out gang war as the evil Sally Bones attempts to control all cats. Horrified and outnumbered, Varjak and the others must fight for their freedom or die trying.