D.J. MacHale 
Pendragon: Blackwater [EPUB ebook] 

Just when Bobby Pendragon thinks he finally understands his purpose as a Traveller he is faced with an impossible choice. Arriving on the beautiful yet primitive territory of Eelong, Bobby finds himself at the bottom of the food chain when he is confronted by the ferocious half-human / half-cat species called Klee. But something is terribly wrong and Bobby soon discovers that the inhabitants of Eelong are in danger of being wiped out by a mysterious plague. In order to save Eelong Bobby realises he must break all Traveller rules endangering himself, his friends and the future of all other territories ~ but can he do it?