Moonspell by Lisanne Harrington

The nightmare of Wolf Creek starts the night of the last full moon in the summer of 2013, and the close-knit little community will never be the same again. Someone—or something—is murdering the townspeople during each month’s full moon. Incredibly, no one connects the murders to the cycle of the moon. At least, not until fourteen-year-old James Manarro is confronted by his eleven-year-old cousin Beth Ann with her suspicions about the identity of the killer. A werewolf. At first, James just laughs it off, but with each vicious murder, he’s forced to admit that Beth may be right…and one, or both, of them might be its next victims.

Book 1 of the Wolf Creek Mysteries