The Werewolf of Fever Swamp - Goosebumps 2nd edition

It started with the strange howling at night. Then there was the dead rabbit. Everyone thinks Grady's new dog is responsible. After all, he looks just like a wolf. But Grady knows his dog is just a regular old dog. And most dogs don't howl at the moon. Or disappear at midnight. Or change into terrifying creatures when the moon is full...