Erin Hunter 
Survivors: The Gathering Darkness #4: Red Moon Rising 

No dog can be trustedand no dog is safe in this gripping fourth book in the second Survivors series.From Erin Hunter, #1 nationally bestselling author of Warriors, Survivors is full of wild and wonderful adventure (Kirkus Reviews, starred review) that will thrill fans of Spirit Animals and Wings of Fire.The Wild Pack is in high spirits after rescuing Alpha and Betas pups. Only Storm believes that danger still walks among themand it wont be long before the traitor dog strikes again. She must convince her Packmates to stand together against the most malicious and elusive enemy they have ever known…before terror and doubt tear them apart.