Erin Hunter 
Survivors Book 2 [PDF ebook] 
A Hidden Enemy

A pulse-pounding animal fantasy series … From the author of the US smash hit series Warriors, confident readers will be enthralled to follow the dog packs as they learn to survive and thrive in a world without human masters. An action-packed series with authentic canine voices that will grip, excite and entertain in equal measure. ‘A Hidden Enemy’ follows Lucky as his loyalties are put to the test. Will he stay loyal to his pack, or will he join a fierce pack of Wild Dogs who are ruled by a menacing half wolf called Alpha? Now it’s time for dogs to rule the world!